Statistics for Business And Economics 8th Edition By Paul Newbold - Test Bank

Statistics for Business And Economics 8th Edition By Paul Newbold – Test Bank

 

Instant Download – Complete Test Bank With Answers

 

 

Sample Questions Are Posted Below

 

Statistics for Business and Economics, 8e (Newbold)

Chapter 5   Continuous Random Variables and Probability Distributions

 

1) The shape of the uniform probability distribution is:

1. A) negatively skewed.
2. B) positively skewed.
3. C) bell-shaped.
4. D) rectangular.

Answer:  D

Difficulty:  Easy

Topic:  Continuous Random Variables

AACSB:  Reflective Thinking Skills

Course LO:  Explain the characteristics and applications of continuous probability distributions

 

2) Sales, investment, consumption, costs, and revenues are economic and business measures which can be represented by:

1. A) discrete variable.
2. B) fixed variables.
3. C) continuous random variables.
4. D) coefficients.

Answer:  C

Difficulty:  Easy

Topic:  Continuous Random Variables

AACSB:  Reflective Thinking Skills

Course LO:  Explain the characteristics and applications of continuous probability distributions

 

3) Because measurements of random variables are rounded to some value, mathematical theory leads us to conclude that in reality, random variables for all applied problems are:

1. A) linear.
2. B) discrete.
3. C) coefficients.
4. D) medians.

Answer:  B

Difficulty:  Easy

Topic:  Continuous Random Variables

AACSB:  Reflective Thinking Skills

Course LO:  Explain the characteristics and applications of continuous probability distributions

 

4) When the distribution of a continuous random variable follows a uniform probability distribution and does not exceed a specific given value, its cumulative distribution function is graphed as a:

1. A) bell-shaped curve.
2. B) polygon.
3. C) rectangle.
4. D) straight line.

Answer:  D

Difficulty:  Moderate

Topic:  Continuous Random Variables

AACSB:  Reflective Thinking Skills

Course LO:  Explain the characteristics and applications of continuous probability distributions

 

5) To obtain the probability that a continuous random variable falls in a specified range, we find the difference between the cumulative probabilities at the lower and upper end of the:

1. A) range.
2. B) median.
3. C) mode.
4. D) mean.

Answer:  A

Difficulty:  Moderate

Topic:  Continuous Random Variables

AACSB:  Reflective Thinking Skills

Course LO:  Explain the characteristics and applications of continuous probability distributions

 

6) A function of continuous random variables which allows for graphical interpretations of their probability structure is called the:

1. A) cumulative distribution function.
2. B) probability density function.
3. C) uniform distribution.
4. D) expected value.

Answer:  B

Difficulty:  Moderate

Topic:  Continuous Random Variables

AACSB:  Reflective Thinking Skills

Course LO:  Explain the characteristics and applications of continuous probability distributions

 

7) The function that may be used to find the probability that the random variable falls within a specific range is called the:

1. A) expected value.
2. B) uniform distribution.
3. C) probability density function.
4. D) linear function.

Answer:  C

Difficulty:  Moderate

Topic:  Continuous Random Variables

AACSB:  Reflective Thinking Skills

Course LO:  Explain the characteristics and applications of continuous probability distributions

 

8) Because the probability of any specific value is 0 for a continuous random variable, the expected values for continuous random variables are computed using:

1. A) Bayes’ Theorem.
2. B) an empirical formula.
3. C) a Venn diagram.
4. D) integral calculus.

Answer:  D

Difficulty:  Moderate

Topic:  Expectations for Continuous Random Variables

AACSB:  Reflective Thinking Skills

Course LO:  Explain the characteristics and applications of continuous probability distributions

 

9) In a random experiment which leads to an outcome that can be represented by a continuous random variable, the average of the values taken as the number of replications becomes infinitely large is called the:

1. A) mode.
2. B) median.
3. C) expected value.
4. D) hypergeometric distribution.

Answer:  C

Difficulty:  Moderate

Topic:  Expectations for Continuous Random Variables

AACSB:  Reflective Thinking Skills

Course LO:  Explain the characteristics and applications of continuous probability distributions

 

10) ________ is the continuous probability distribution used most often for economics and business applications.

1. A) Normal probability distribution
2. B) Uniform distribution
3. C) Exponential distribution
4. D) Incremental distribution

Answer:  A

Difficulty:  Moderate

Topic:  The Normal Distribution

AACSB:  Reflective Thinking Skills

Course LO:  Explain the characteristics and applications of continuous probability distributions

 

11) The shape of the normal probability density function is a symmetric bell-shaped curve centered on the:

1. A) variance.
2. B) standard deviation.
3. C) coefficient.
4. D) mean.

Answer:  D

Difficulty:  Moderate

Topic:  The Normal Distribution

AACSB:  Reflective Thinking Skills

Course LO:  Explain the characteristics and applications of continuous probability distributions

 

12) We can convert any normal distribution to a distribution with a mean 0 and a variance 1. What is the distribution called?

1. A) Poisson distribution
2. B) standard normal distribution
3. C) hypergeometric distribution
4. D) marginal distribution

Answer:  B

Difficulty:  Moderate

Topic:  The Normal Distribution

AACSB:  Reflective Thinking Skills

Course LO:  Explain the characteristics and applications of continuous probability distributions

 

13) To approximate a discrete distribution that has many different outcomes useful in most applied business and economic problems, we are, in fact, using the:

1. A) Poisson distribution.
2. B) normal distribution.
3. C) Hypergeometric distribution.
4. D) marginal distribution.

Answer:  B

Difficulty:  Moderate

Topic:  The Normal Distribution

AACSB:  Reflective Thinking Skills

Course LO:  Explain the characteristics and applications of continuous probability distributions

 

14) In computing probabilities for proportion or percentage intervals, we use a direct extension of the normal distribution approximation for the:

1. A) Poisson distribution.
2. B) hypergeometric distribution.
3. C) binomial distribution.
4. D) uniform distribution.

Answer:  C

Difficulty:  Moderate

Topic:  Normal Distribution Approximation for Binomial Distribution

AACSB:  Reflective Thinking Skills

Course LO:  Explain the characteristics and applications of continuous probability distributions

 

15) Let the random variable Z follow a standard normal distribution. Find P(0 < Z < 0.57).

1. A) 0.2843
2. B) 0.7843
3. C) 0.2157
4. D) 0.7157

Answer:  C

Difficulty:  Moderate

Topic:  The Normal Distribution

AACSB:  Analytic Skills

Course LO:  Explain the characteristics and applications of continuous probability distributions

 

16) Suppose that 19% of all sales are for amounts greater than $1,000. In a random sample of 30 invoices, what is the probability that more than six of the invoices are for over $1,000? Use the binomial approximation for the normal distribution.

1. A) 0.4443
2. B) 0.9440
3. C) 0.5557
4. D) 0.0560

Answer:  A

Difficulty:  Moderate

Topic:  Normal Distribution Approximation for Binomial Distribution

AACSB:  Analytic Skills

Course LO:  Explain the characteristics and applications of continuous probability distributions

 

17) The area under the probability density function for the uniform distribution is between:

1. A) -∞ and +∞.
2. B) 0 and 1.
3. C) ± three standard deviations from the mean of the distribution.
4. D) the maximum and minimum values of the random variable.

Answer:  D

Difficulty:  Easy

Topic:  Continuous Random Variables

AACSB:  Reflective Thinking Skills

Course LO:  Explain the characteristics and applications of continuous probability distributions

 

18) Let the random variable Z follow a standard normal distribution. Find the value k, such that P(Z > k) = 0.39.

1. A) 0.28
2. B) 1.23
3. C) -1.23
4. D) -0.28

Answer:  A

Difficulty:  Moderate

Topic:  The Normal Distribution

AACSB:  Analytic Skills

Course LO:  Explain the characteristics and applications of continuous probability distributions

 

19) Let the random variable Z follow a standard normal distribution. Find P(-2.21 < Z < 0).

1. A) 0.9864
2. B) 0.4864
3. C) 0.0136
4. D) 0.5136

Answer:  B

Difficulty:  Moderate

Topic:  The Normal Distribution

AACSB:  Analytic Skills

Course LO:  Explain the characteristics and applications of continuous probability distributions

 

20) The continuous random variable X is uniformly distributed over the interval [a, b]. The mean of the probability distribution of X is:

1. A) (a + b) / 2
2. B) n – ab
3. C) (b – a) / 2
4. D) (a + b) / n

Answer:  A

Difficulty:  Moderate

Topic:  Continuous Random Variables

AACSB:  Reflective Thinking Skills

Course LO:  Explain the characteristics and applications of continuous probability distributions

 

21) Investment A has an expected return of 7.8% with a standard deviation of 2%. Investment B has an expected return of 7.2% with a standard deviation of 3.1%. Which stock is more likely to have a return greater than 10%?

1. A) Stock A
2. B) Stock B
3. C) The probability is the same for both A and B.
4. D) Unable to determine.

Answer:  B

Difficulty:  Moderate

Topic:  The Normal Distribution

AACSB:  Analytic Skills

Course LO:  Explain the characteristics and applications of continuous probability distributions

 

22) What does the uniform and normal probability distribution have in common?

1. A) Both have the same standard deviation.
2. B) The mean, median, and mode are equal for each.
3. C) About 68% of the observations are within one standard deviation of the mean.
4. D) The uniform distribution uses discrete data; the normal distribution is based on continuous data.

Answer:  B

Difficulty:  Moderate

Topic:  Continuous Random Variables

AACSB:  Reflective Thinking Skills

Course LO:  Explain the characteristics and applications of continuous probability distributions

 

23) Let the random variable Z follow a standard normal distribution. Find P(-1.33 < Z < 0.78).

1. A) 0.6905
2. B) 0.2823
3. C) 0.2177
4. D) 0.3095

Answer:  A

Difficulty:  Moderate

Topic:  The Normal Distribution

AACSB:  Analytic Skills

Course LO:  Explain the characteristics and applications of continuous probability distributions

 

THE NEXT QUESTIONS ARE BASED ON THE FOLLOWING INFORMATION:

You have recently joined a country club. The number of times you expect to play golf in a month is represented by a random variable with a mean of 10 and a standard deviation of 2.2. Assume you pay monthly membership fees of $500 per month and pay an additional $50 per round of golf.

 

24) What is your average monthly bill from the country club?

1. A) $700
2. B) $800
3. C) $900
4. D) $1000

Answer:  D

Difficulty:  Moderate

Topic:  The Normal Distribution

AACSB:  Analytic Skills

Course LO:  Explain the characteristics and applications of continuous probability distributions

 

25) What is the standard deviation for your average monthly bill from the country club?

1. A) $220
2. B) $110
3. C) $324
4. D) $180

Answer:  B

Difficulty:  Moderate

Topic:  The Normal Distribution

AACSB:  Analytic Skills

Course LO:  Explain the characteristics and applications of continuous probability distributions

 

26) Which of the following is false regarding the normal distribution?

1. A) The mean, median, and mode are equal.
2. B) The frequency of values peaks at the mean, regardless of the value of the mean or variance.
3. C) 100% of the values fall between ±3 standard deviations.
4. D) The shape of the distribution is symmetrical around the mean.

Answer:  C

Difficulty:  Moderate

Topic:  The Normal Distribution

AACSB:  Reflective Thinking Skills

Course LO:  Explain the characteristics and applications of continuous probability distributions

 

27) One normal distribution has a mean of 5 and a standard deviation of 2. A second normal distribution has a mean of 6 and a standard deviation of 1. Which of the following statements is true?

1. A) The width of the first distribution is wider than the second distribution.
2. B) The central location of the first distribution is higher than the second distribution.
3. C) The dispersions of both distributions are the same.
4. D) The locations of both distributions are the same.

Answer:  A

Difficulty:  Easy

Topic:  The Normal Distribution

AACSB:  Analytic Skills

Course LO:  Explain the characteristics and applications of continuous probability distributions

 

28) Let the random variable Z follow a standard normal distribution. Find the value k, such
that P(Z > k) = 0.73.

1. A) 0.27
2. B) 0.73
3. C) -0.16
4. D) -0.61

Answer:  D

Difficulty:  Moderate

Topic:  The Normal Distribution

AACSB:  Analytic Skills

Course LO:  Explain the characteristics and applications of continuous probability distributions

 

THE NEXT QUESTIONS ARE BASED ON THE FOLLOWING INFORMATION:

Let the random variable X follow a normal distribution with a mean of 17.1 and a standard deviation of 3.2.

 

29) What is P(X > 16)?

1. A) 0.3401
2. B) 0.6331
3. C) 0.3669
4. D) 0.8326

Answer:  B

Difficulty:  Moderate

Topic:  The Normal Distribution

AACSB:  Analytic Skills

Course LO:  Explain the characteristics and applications of continuous probability distributions

 

30) What is P(15 < X < 20)?

1. A) 0.5581
2. B) 0.1814
3. C) 0.5640
4. D) 0.2546

Answer:  C

Difficulty:  Moderate

Topic:  The Normal Distribution

AACSB:  Analytic Skills

Course LO:  Explain the characteristics and applications of continuous probability distributions

 

31) The mean of a normally distributed group of weekly incomes for a group of executives is $2,400 and the standard deviation is $600. What is the z-score for an income of $1,500/week?

1. A) -1.5
2. B) -1.0
3. C) 2.5
4. D) 1.9

Answer:  A

Difficulty:  Moderate

Topic:  The Normal Distribution

AACSB:  Analytic Skills

Course LO:  Explain the characteristics and applications of continuous probability distributions

 

32) Let the random variable Z follow a standard normal distribution. Find the value k, such
that P(-0.62 < Z < k) = 0.43.

1. A) 0.20
2. B) 0.52
3. C) 0.12
4. D) 0.56

Answer:  B

Difficulty:  Moderate

Topic:  The Normal Distribution

AACSB:  Analytic Skills

Course LO:  Explain the characteristics and applications of continuous probability distributions

 

33) The normal probabilities are calculated using the table of standard normal distribution where the mean and standard deviations are, respectively:

1. A) 1 and 1.
2. B) 10 and 0.
3. C) 0 and 1.
4. D) 0 and 10.

Answer:  C

Difficulty:  Moderate

Topic:  The Normal Distribution

AACSB:  Analytic Skills

Course LO:  Explain the characteristics and applications of continuous probability distributions

 

THE NEXT QUESTIONS ARE BASED ON THE FOLLOWING INFORMATION:

Let the random variable Z follow a standard normal distribution.

 

34) What is P(Z > 1.2)?

1. A) 0.1112
2. B) 0.8849
3. C) 0.1151
4. D) 0.6112

Answer:  C

Difficulty:  Moderate

Topic:  The Normal Distribution

AACSB:  Analytic Skills

Course LO:  Explain the characteristics and applications of continuous probability distributions

 

35) What is P(Z > -0.21)?

1. A) 0.4207
2. B) 0.4168
3. C) 0.5793
4. D) 0.5832

Answer:  D

Difficulty:  Moderate

Topic:  The Normal Distribution

AACSB:  Analytic Skills

Course LO:  Explain the characteristics and applications of continuous probability distributions

 

36) What is P(0.33 < Z < 0.45)?

1. A) 0.5443
2. B) 0.0443
3. C) 0.4557
4. D) 0.1515

Answer:  B

Difficulty:  Moderate

Topic:  The Normal Distribution

AACSB:  Analytic Skills

Course LO:  Explain the characteristics and applications of continuous probability distributions

 

37) The distribution of annual incomes of a sample of college graduates is normally distributed with a mean of $52,000 and a standard deviation of 1,000. About 68 percent of the incomes lie between what two income levels?

1. A) 52,000 and 62,000
2. B) 50,000 and 60,000
3. C) 51,000 and 53,000
4. D) 53,000 and 57,000

Answer:  C

Difficulty:  Moderate

Topic:  The Normal Distribution

AACSB:  Analytic Skills

Course LO:  Explain the characteristics and applications of continuous probability distributions

 

THE NEXT QUESTIONS ARE BASED ON THE FOLLOWING INFORMATION:

Let the random variable X follow a normal distribution with a mean of 61.7 and a standard deviation of 5.2.

 

38) What is the value of k such that P(X > k) = 0.63?

59. A) 59.984
60. B) 66.446
61. C) 62.830
62. D) 67.576

Answer:  A

Difficulty:  Moderate

Topic:  The Normal Distribution

AACSB:  Analytic Skills

Course LO:  Explain the characteristics and applications of continuous probability distributions

 

39) What is the value of k such that P(59 < X < k) = 0.54?

65. A) 65.8
66. B) 64.6
67. C) 63.7
68. D) 66.9

Answer:  D

Difficulty:  Moderate

Topic:  The Normal Distribution

AACSB:  Analytic Skills

Course LO:  Explain the characteristics and applications of continuous probability distributions

 

40) What proportion of the total area under the normal curve is within ± two standard deviations of the mean?

1. A) About 50%
2. B) About 68%
3. C) About 95%
4. D) About 99.7%

Answer:  C

Difficulty:  Moderate

Topic:  The Normal Distribution

AACSB:  Analytic Skills

Course LO:  Explain the characteristics and applications of continuous probability distributions

 

THE NEXT QUESTIONS ARE BASED ON THE FOLLOWING INFORMATION:

The number of orders that come into a mail-order sales office each month is normally distributed with a mean of 298 and a standard deviation of 15.4.

 

41) What is the probability that in a particular month the office receives more than 310 orders?

1. A) 0.7823
2. B) 0.2826
3. C) 0.7174
4. D) 0.2177

Answer:  D

Difficulty:  Moderate

Topic:  The Normal Distribution

AACSB:  Analytic Skills

Course LO:  Explain the characteristics and applications of continuous probability distributions

 

42) The probability is 0.3 that the sales office receives less than how many orders?

310. A) 310.9
311. B) 285.1
312. C) 290.0
313. D) 306.0

Answer:  C

Difficulty:  Moderate

Topic:  The Normal Distribution

AACSB:  Analytic Skills

Course LO:  Explain the characteristics and applications of continuous probability distributions

 

43) What is the area under the normal curve between Z = 1.0 and Z = 2.0?

1. A) 0.0228
2. B) 0.1359
3. C) 0.3413
4. D) 0.4772

Answer:  B

Difficulty:  Moderate

Topic:  The Normal Distribution

AACSB:  Analytic Skills

Course LO:  Explain the characteristics and applications of continuous probability distributions

 

44) What is the area under the normal curve between Z = -2 and Z = 0?

1. A) 0.5000
2. B) 0.6826
3. C) 0.1359
4. D) 0.4772

Answer:  D

Difficulty:  Moderate

Topic:  The Normal Distribution

AACSB:  Analytic Skills

Course LO:  Explain the characteristics and applications of continuous probability distributions

 

45) What proportion of the total area under the normal curve is above the mean?

1. A) 50%
2. B) 68%
3. C) 95%
4. D) 99.7%

Answer:  A

Difficulty:  Moderate

Topic:  The Normal Distribution

AACSB:  Reflective Thinking Skills

Course LO:  Explain the characteristics and applications of continuous probability distributions

 

THE NEXT QUESTIONS ARE BASED ON THE FOLLOWING INFORMATION:

The amount of time you have to wait at a particular stoplight is uniformly distributed between zero and two minutes.

 

46) What is the probability that you have to wait more than 30 seconds for the stoplight?

1. A) 0.25
2. B) 0.50
3. C) 0.75
4. D) 1.01

Answer:  C

Difficulty:  Moderate

Topic:  Continuous Random Variables

AACSB:  Analytic Skills

Course LO:  Explain the characteristics and applications of continuous probability distributions

 

47) What is the probability that you have to wait between 15 and 45 seconds for the stoplight?

1. A) 0.15
2. B) 0.25
3. C) 0.35
4. D) 0.45

Answer:  B

Difficulty:  Moderate

Topic:  Continuous Random Variables

AACSB:  Analytic Skills

Course LO:  Explain the characteristics and applications of continuous probability distributions

 

48) Eighty percent of the time, the stoplight will change before you have to wait X seconds, what is the value of X?

1. A) 90 seconds
2. B) 24 seconds
3. C) 30 seconds
4. D) 96 seconds

Answer:  D

Difficulty:  Moderate

Topic:  Continuous Random Variables

AACSB:  Analytic Skills

Course LO:  Explain the characteristics and applications of continuous probability distributions

 

49) Sixty percent of the time, the stoplight will change before you have to wait X seconds, what is the value of X?

1. A) 72 seconds
2. B) 60 seconds
3. C) 48 seconds
4. D) 36 seconds

Answer:  A

Difficulty:  Moderate

Topic:  Continuous Random Variables

AACSB:  Analytic Skills

Course LO:  Explain the characteristics and applications of continuous probability distributions

 

50) The median score for the final exam in a chemistry class was 75 and 18% of the students received a grade greater than 80. If the test scores were normally distributed, what is the probability that a randomly selected exam had a score between 75 and 80?

1. A) 68%
2. B) 32%
3. C) 80%
4. D) 50%

Answer:  B

Difficulty:  Moderate

Topic:  The Normal Distribution

AACSB:  Analytic Skills

Course LO:  Explain the characteristics and applications of continuous probability distributions

 

THE NEXT QUESTIONS ARE BASED ON THE FOLLOWING INFORMATION:

The length of time it takes to be seated at a local restaurant on Friday night is normally distributed with a mean of 15 minutes and a standard deviation of 4.75 minutes.

 

51) What is the probability that you have to wait more than 20 minutes to be seated?

1. A) 0.1761
2. B) 0.3531
3. C) 0.6761
4. D) 0.1469

Answer:  D

Difficulty:  Moderate

Topic:  The Normal Distribution

AACSB:  Analytic Skills

Course LO:  Explain the characteristics and applications of continuous probability distributions

 

52) What is the probability that you have to wait between 13 and 16 minutes to be seated?

1. A) 0.083
2. B) 0.246
3. C) 0.163
4. D) 0.663

Answer:  B

Difficulty:  Moderate

Topic:  The Normal Distribution

AACSB:  Analytic Skills

Course LO:  Explain the characteristics and applications of continuous probability distributions

 

53) A fair coin is flipped 100 times. The probability of obtaining between 40 and 60 heads is approximately:

1. A) 0.6826
2. B) 0.7518
3. C) 0.9544
4. D) 0.9973

Answer:  C

Difficulty:  Moderate

Topic:  Normal Distribution Approximation for Binomial Distribution

AACSB:  Analytic Skills

Course LO:  Explain the characteristics and applications of continuous probability distributions

 

THE NEXT QUESTIONS ARE BASED ON THE FOLLOWING INFORMATION:

Investment A has an expected return of 8% with a standard deviation of 2.5%. Investment B has an expected return of 6% with a standard deviation of 1.2%. Assume you invest equally in both investments and that the rates of return are independent.

 

54) What is the expected return of your portfolio?

1. A) 8%
2. B) 7%
3. C) 6%
4. D) 4%

Answer:  B

Difficulty:  Moderate

Topic:  Jointly Distributed Continuous Random Variables

AACSB:  Analytic Skills

Course LO:  Explain the characteristics and applications of continuous probability distributions

 

55) What is the standard deviation of the return on your portfolio? Assume that the returns on the two investments are independent.

2. A) 2.77
3. B) 2.50
4. C) 7.69
5. D) 6.25

Answer:  A

Difficulty:  Moderate

Topic:  Jointly Distributed Continuous Random Variables

AACSB:  Analytic Skills

Course LO:  Explain the characteristics and applications of continuous probability distributions

 

56) A hospital finds that 20% of its accounts are at least 60 days in arrears. A random sample of 500 accounts was taken. What is the probability that fewer than 120 accounts in the sample were at least 60 days in arrears?

1. A) 0.9875
2. B) 0.4875
3. C) 0.5125
4. D) 0.0125

Answer:  A

Difficulty:  Moderate

Topic:  Normal Distribution Approximation for Binomial Distribution

AACSB:  Analytic Skills

Course LO:  Explain the characteristics and applications of continuous probability distributions

 

THE NEXT QUESTIONS ARE BASED ON THE FOLLOWING INFORMATION:

You are the webmaster for your firm’s web-site. From your records, you know that the probability that a visitor will buy something from your firm is 0.23. In one day, the number of visitors is 952.

 

57) What is the probability that less than 200 of them will buy something from your firm? Use the normal approximation to the binomial.

1. A) 0.4279
2. B) 0.5721
3. C) 0.9279
4. D) 0.0721

Answer:  D

Difficulty:  Moderate

Topic:  Jointly Distributed Continuous Random Variables

AACSB:  Analytic Skills

Course LO:  Explain the characteristics and applications of continuous probability distributions

 

58) What is the probability that at least 210 of them will buy something from your firm? Use the normal approximation to the binomial.

1. A) 0.7549
2. B) 0.2549
3. C) 0.2451
4. D) 0.7451

Answer:  A

Difficulty:  Moderate

Topic:  Jointly Distributed Continuous Random Variables

AACSB:  Analytic Skills

Course LO:  Explain the characteristics and applications of continuous probability distributions

 

59) Let X1, X2,……,Xk be a set of k continuous random variables. The function F(x1, x2, …..,xk)which defines the probability that simultaneously X1 < x1, X2 < x2 and so on is called a:

1. A) marginal distribution function.
2. B) marginal cumulative distribution function.
3. C) joint cumulative distribution function.
4. D) normal distribution function.

Answer:  C

Difficulty:  Moderate

Topic:  Jointly Distributed Continuous Random Variables

AACSB:  Reflective Thinking Skills

Course LO:  Explain the characteristics and applications of continuous probability distributions

 

60) Let the random variable Z follow a standard normal distribution. Find the value k, such
that P(-k < Z < k) = 0.78.

1. A) 1.78
2. B) 1.37
3. C) 1.23
4. D) 0.78

Answer:  C

Difficulty:  Moderate

Topic:  The Normal Distribution

AACSB:  Analytic Skills

Course LO:  Explain the characteristics and applications of continuous probability distributions

 

61) Checkout times in a Walmart store follow an exponential distribution with a mean time of 8 minutes. What is the probability that the checkout time for the next customer will be 6 minutes or less?

1. A) 0.528
2. B) 0.472
3. C) 0.972
4. D) 0.328

Answer:  A

Difficulty:  Moderate

Topic:  The Exponential Distribution

AACSB:  Analytic Skills

Course LO:  Explain the characteristics and applications of continuous probability distributions

 

62) Which type of distribution would best model the waiting times of the departing flights at JFK international airport?

1. A) The uniform distribution
2. B) The normal distribution
3. C) The binomial distribution
4. D) The exponential distribution

Answer:  D

Difficulty:  Moderate

Topic:  The Exponential Distribution

AACSB:  Reflective Thinking Skills

Course LO:  Explain the characteristics and applications of continuous probability distributions

 

63) During a professor’s office hours, students arrive, on average, every ten minutes. Assume that the distribution of the time between arrivals follows an exponential distribution. Suppose that a student has just left.

 

What is the probability that the professor has more than 20 minutes before the next student shows up?

1. A) 0.8187
2. B) 0.8647
3. C) 0.1353
4. D) 0.1813

Answer:  C

Difficulty:  Moderate

Topic:  The Exponential Distribution

AACSB:  Analytic Skills

Course LO:  Explain the characteristics and applications of continuous probability distributions

 

THE NEXT QUESTIONS ARE BASED ON THE FOLLOWING INFORMATION:

Let X be a continuous random variable with mean of 1200 and standard deviation of 250. Define the random variable Y as follows: Y = 80 + 0.05X

 

64) What is the mean of Y?

1. A) 680
2. B) 330
3. C) 120
4. D) 140

Answer:  D

Difficulty:  Moderate

Topic:  Expectations for Continuous Random Variables

AACSB:  Analytic Skills

Course LO:  Explain the characteristics and applications of continuous probability distributions

 

65) What is the standard deviation of Y?

92. A) 92.5
93. B) 55.9
94. C) 12.5
95. D) 11.89

Answer:  C

Difficulty:  Moderate

Topic:  Expectations for Continuous Random Variables

AACSB:  Analytic Skills

Course LO:  Explain the characteristics and applications of continuous probability distributions

 

THE NEXT QUESTIONS ARE BASED ON THE FOLLOWING INFORMATION:

The time it takes to assemble an electronic component is normally distributed with a mean of 17.2 minutes and a standard deviation of 3.1 minutes.

 

66) The probability is 95% that it will take at least how long to assemble a component?

12. A) 12.7
13. B) 11.7
14. C) 12.1
15. D) 11.1

Answer:  C

Difficulty:  Moderate

Topic:  The Normal Distribution

AACSB:  Analytic Skills

Course LO:  Explain the characteristics and applications of continuous probability distributions

 

67) What is the probability that it will take at least 16 minutes to assemble a component?

1. A) 0.8483
2. B) 0.3483
3. C) 0.1517
4. D) 0.6517

Answer:  D

Difficulty:  Moderate

Topic:  The Normal Distribution

AACSB:  Analytic Skills

Course LO:  Explain the characteristics and applications of continuous probability distributions

 

68) The median score for the final exam in a statistics class was 85 and 20 percent of the students received a grade greater than 90. What is the probability that a randomly selected exam had a score between 85 and 90?

1. A) 80 percent
2. B) 30 percent
3. C) 50 percent
4. D) There is not sufficient information to answer this question.

Answer:  B

Difficulty:  Moderate

Topic:  The Normal Distribution

AACSB:  Analytic Skills

Course LO:  Explain the characteristics and applications of continuous probability distributions

 

THE NEXT QUESTIONS ARE BASED ON THE FOLLOWING INFORMATION:

Sales at a local wholesaler consist of both retail as well as online sales. During the course of a month, retail sales have a mean of $96,780 with a standard deviation of $12,520. Over the same time period, online sales average $229,620 with a standard deviation of $23,100. Assume that the retail sales are independent of online sales.

 

69) What is the mean of the wholesaler’s monthly sales?

1. A) $326,400
2. B) $135,620
3. C) $132,840
4. D) $163,200

Answer:  A

Difficulty:  Moderate

Topic:  Jointly Distributed Continuous Random Variables

AACSB:  Analytic Skills

Course LO:  Explain the characteristics and applications of continuous probability distributions

 

70) What is the standard deviation of the wholesaler monthly sales?

620. A) $35,620.0
621. B) $26,274.7
622. C) $71,240.0
623. D) $68,960.3

Answer:  B

Difficulty:  Moderate

Topic:  Jointly Distributed Continuous Random Variables

AACSB:  Analytic Skills

Course LO:  Explain the characteristics and applications of continuous probability distributions

 

71) A car owner determines that annual repair costs (R) can be estimated based on the number of miles driven in one year (M) through the expression R = 800 + 0.05M. If the average number of miles driven is 12000 with a standard deviation of 2500 miles, what is the standard deviation of the expected annual repair costs?

1. A) 1400
2. B) 925
3. C) 800
4. D) 125

Answer:  D

Difficulty:  Moderate

Topic:  Expectations for Continuous Random Variables

AACSB:  Analytic Skills

Course LO:  Explain the characteristics and applications of continuous probability distributions

 

THE NEXT QUESTIONS ARE BASED ON THE FOLLOWING INFORMATION:

The number of nails in a five-pound box of nails is normally distributed with a mean of 563.3 and a standard deviation of 33.2.

 

72) What is the probability that there are less than 500 nails in a randomly-selected five-pound box of nails?

1. A) 0.5287
2. B) 0.4730
3. C) 0.0281
4. D) 0.9713

Answer:  C

Difficulty:  Moderate

Topic:  Expectations for Continuous Random Variables

AACSB:  Analytic Skills

Course LO:  Explain the characteristics and applications of continuous probability distributions

 

73) What is the probability that there are between 525 and 575 nails in a randomly-selected five-pound box of nails?

1. A) 0.5117
2. B) 0.4883
3. C) 0.5526
4. D) 0.4474

Answer:  A

Difficulty:  Moderate

Topic:  Expectations for Continuous Random Variables

AACSB:  Analytic Skills

Course LO:  Explain the characteristics and applications of continuous probability distributions

 

74) The probability is 0.99 that a randomly-selected five-pound box of nails contains at least how many nails approximately?

1. A) 641
2. B) 486
3. C) 503
4. D) 624

Answer:  B

Difficulty:  Moderate

Topic:  Expectations for Continuous Random Variables

AACSB:  Analytic Skills

Course LO:  Explain the characteristics and applications of continuous probability distributions

 

75) A two-dimensional plot of the observed data values on the vertical-axis with their corresponding quartile values from a standardized normal distribution on the horizontal-axis is referred to as a:

1. A) normal probability plot.
2. B) quartile plot.
3. C) normal probability distribution.
4. D) normal-quartile plot.

Answer:  A

Difficulty:  Moderate

Topic:  The Normal Distribution

AACSB:  Reflective Thinking Skills

Course LO:  Explain the characteristics and applications of continuous probability distributions

 

76) Which of the following is not a characteristic for a normal distribution?

1. A) It is symmetrical distribution.
2. B) The mean is always zero.
3. C) The mean, median, and mode are all equal.
4. D) It is a bell-shaped distribution.

Answer:  B

Difficulty:  Moderate

Topic:  The Normal Distribution

AACSB:  Reflective Thinking Skills

Course LO:  Explain the characteristics and applications of continuous probability distributions

 

77) Let the random variable Z follow a standard normal distribution. The total probability to the right of Z = 2.18 and to the left of Z = -1.75 is:

1. A) 0.4854
2. B) 0.4599
3. C) 0.0146
4. D) 0.0547

Answer:  D

Difficulty:  Moderate

Topic:  The Normal Distribution

AACSB:  Analytic Skills

Course LO:  Explain the characteristics and applications of continuous probability distributions

 

78) The speed of cars passing through a check point follows a normal distribution with a mean of 45 miles per hour and a standard deviation of 6 miles per hour. What is the probability that the next car passing will be exceeding 51 miles per hour?

1. A) 0.9854
2. B) 0.8413
3. C) 0.7967
4. D) 0.1587

Answer:  D

Difficulty:  Moderate

Topic:  The Normal Distribution

AACSB:  Analytic Skills

Course LO:  Explain the characteristics and applications of continuous probability distributions

 

79) Let the random variable Z follow a standard normal distribution, and let z1 be a possible value of Z that is unknown but identifiable by position and area. Find z1 if the area to the right of z1 is 0.8413.

1. A) 1.00
2. B) -1.00
3. C) 0.00
4. D) 0.41

Answer:  B

Difficulty:  Moderate

Topic:  The Normal Distribution

AACSB:  Analytic Skills

Course LO:  Explain the characteristics and applications of continuous probability distributions

 

80) Given that X is a normally distributed random variable with a mean of 52 and a standard deviation of 2, the probability that X is between 48 and 56 is:

1. A) 0.0896
2. B) 0.4104
3. C) 0.5896
4. D) 0.9544

Answer:  D

Difficulty:  Moderate

Topic:  The Normal Distribution

AACSB:  Analytic Skills

Course LO:  Explain the characteristics and applications of continuous probability distributions

 

81) Let the random variable Z follow a standard normal distribution, and let z1 be a possible value of Z that is unknown but identifiable by position and area. Find z1 if the symmetrical area between a negative z1 and a positive z1 is 0.9544.

2. A) 2.00
3. B) 0.11
4. C) 2.50
5. D) 0.06

Answer:  A

Difficulty:  Moderate

Topic:  The Normal Distribution

AACSB:  Analytic Skills

Course LO:  Explain the characteristics and applications of continuous probability distributions

 

82) Let the random variable Z follow a standard normal distribution, and let z1 be a possible value of Z that is unknown but identifiable by position and area. Find z1 if the area to the right of z1 is 0.0869.

1. A) -1.36
2. B) 1.71
3. C) 1.36
4. D) 1.80

Answer:  C

Difficulty:  Moderate

Topic:  The Normal Distribution

AACSB:  Analytic Skills

Course LO:  Explain the characteristics and applications of continuous probability distributions

 

83) Checkout times in a grocery store follow the exponential distribution with a mean time of 6.5 minutes. What is the probability that the checkout time (T) for the next customer will be less than 5 minutes?

1. A) 0.537
2. B) 0.463
3. C) 0.257
4. D) 0.950

Answer:  A

Difficulty:  Moderate

Topic:  The Exponential Distribution

AACSB:  Analytic Skills

Course LO:  Explain the characteristics and applications of continuous probability distributions

 

84) Let the random variable Z follow a standard normal distribution, and let z1 be a possible value of Z that is representing the 10th percentile of the standard normal distribution. Find the value of z1.

1. A) 0.255
2. B) -0.255
3. C) 1.28
4. D) -1.28

Answer:  D

Difficulty:  Moderate

Topic:  The Normal Distribution

AACSB:  Analytic Skills

Course LO:  Explain the characteristics and applications of continuous probability distributions

 

85) Let the random variable Z follow a standard normal distribution, and let z1be a possible value of Z that is representing the 75th percentile of the standard normal distribution. Find the value of z1.

1. A) 0.67
2. B) -0.67
3. C) 1.28
4. D) -1.28

Answer:  A

Difficulty:  Moderate

Topic:  The Normal Distribution

AACSB:  Analytic Skills

Course LO:  Explain the characteristics and applications of continuous probability distributions

 

86) Suppose the likelihood that someone who logs onto a particular site on the Internet will purchase an item is 0.10. If the site has 200 people accessing it in the next day, what is the probability that less than 24 customers will make a purchase?

1. A) 0.5008
2. B) 0.1736
3. C) 0.8264
4. D) 0.2461

Answer:  C

Difficulty:  Moderate

Topic:  Normal Distribution Approximation for Binomial Distribution

AACSB:  Analytic Skills

Course LO:  Explain the characteristics and applications of continuous probability distributions

 

87) Let the random variable Z follow a standard normal distribution, and let z1be a possible value of Z that is representing the 90th percentile of the standard normal distribution. Find the value of z1.

1. A) 0.67
2. B) -1.28
3. C) 1.28
4. D) -0.67

Answer:  C

Difficulty:  Moderate

Topic:  The Normal Distribution

AACSB:  Analytic Skills

Course LO:  Explain the characteristics and applications of continuous probability distributions

 

88) The owner of a fish market determined that the average weight for a catfish is 3.4 pounds with a standard deviation of 0.8 of a pound. A citation catfish should be one of the top 2% in weight. Assuming the weights of catfish are normally distributed, at what weight (in pounds) should the citation designation be established?

1. A) 1.65 pounds
2. B) 5.04 pounds
3. C) 5.42 pounds
4. D) 6.76 pounds

Answer:  B

Difficulty:  Moderate

Topic:  The Normal Distribution

AACSB:  Analytic Skills

Course LO:  Explain the characteristics and applications of continuous probability distributions

 

89) A very large logging operation has serious problems keeping their skidders operating properly. The equipment fails at the rate of 3 breakdowns every 48 hours. Assume that x is time between breakdowns and is exponentially distributed. The probability of a single breakdown within 24 hours is:

1. A) 0.0498
2. B) 0.7769
3. C) 0.2231
4. D) 0.9502

Answer:  B

Difficulty:  Challenging

Topic:  The Exponential Distribution

AACSB:  Analytic Skills

Course LO:  Explain the characteristics and applications of continuous probability distributions

 

90) If the mean of an exponential distribution is 2, then the value of the parameter λ is:

4. A) 4.0
5. B) 2.2
6. C) 1.0
7. D) 0.5

Answer:  D

Difficulty:  Moderate

Topic:  The Exponential Distribution

AACSB:  Analytic Skills

Course LO:  Explain the characteristics and applications of continuous probability distributions

 

91) A catalog company administered a survey to determine how long customers were willing to wait on hold before ordering a product. The length of time was found to be a random variable best approximated by an exponential distribution with a mean equal to 3.5 minutes. What proportion of customers having to hold more than 5.0 minutes will hang up before placing an order?

1. A) 0.2397
2. B) 0.5714
3. C) 0.4286
4. D) 0.7603

Answer:  A

Difficulty:  Moderate

Topic:  The Exponential Distribution

AACSB:  Analytic Skills

Course LO:  Explain the characteristics and applications of continuous probability distributions

 

92) If the random variable x is exponentially distributed with parameter λ = 1.5, then the
probability P(2 ≤ X ≤ 4) is equal to:

1. A) 0.6667
2. B) 0.5000
3. C) 0.0473
4. D) 0.2500

Answer:  C

Difficulty:  Moderate

Topic:  The Exponential Distribution

AACSB:  Analytic Skills

Course LO:  Explain the characteristics and applications of continuous probability distributions

 

93) Which of the following is not true for an exponential distribution with parameter λ?

1. A) Mean = 1/λ
2. B) Standard deviation = 1/λ
3. C) The distribution is completely determined once the value of λ is known.
4. D) The distribution is symmetric around the mean.

Answer:  D

Difficulty:  Moderate

Topic:  The Exponential Distribution

AACSB:  Reflective Thinking Skills

Course LO:  Explain the characteristics and applications of continuous probability distributions

 

94) If the random variable X is exponentially distributed with parameter λ = 4, then the
probability P(X ≤ 0.25) is equal to:

1. A) 0.6321
2. B) 0.3679
3. C) 0.2500
4. D) 0.5000

Answer:  A

Difficulty:  Moderate

Topic:  The Exponential Distribution

AACSB:  Analytic Skills

Course LO:  Explain the characteristics and applications of continuous probability distributions

 

95) Which of the following is not a continuous distribution?

1. A) normal distribution
2. B) exponential distribution
3. C) uniform distribution
4. D) Poisson distribution

Answer:  D

Difficulty:  Moderate

Topic:  Continuous Random Variables

AACSB:  Reflective Thinking Skills

Course LO:  Explain the characteristics and applications of continuous probability distributions

 

96) If Z is a standard normal random variable, the area between Z = 0.0 and Z = 1.25 compared to the area between Z = 1.25 and Z = 2.5 will be:

1. A) smaller.
2. B) larger.
3. C) the same.
4. D) There is not enough information to answer this question.

Answer:  B

Difficulty:  Moderate

Topic:  The Normal Distribution

AACSB:  Analytic Skills

Course LO:  Explain the characteristics and applications of continuous probability distributions

97) If X is a normal random variable with mean of 1228 and a standard deviation of 120, the number of standard deviations from 1228 to 1380 is:

10. A) 10.233
11. B) 3.1989
12. C) 11.50
13. D) 1.267

Answer:  D

Difficulty:  Moderate

Topic:  The Normal Distribution

AACSB:  Analytic Skills

Course LO:  Explain the characteristics and applications of continuous probability distributions

 

98) If the continuous random variable X is uniformly distributed over the interval 6 to 10, then the height of this distribution, f(x), is:

1. A) 0.125
2. B) 0.250
3. C) 0.500
4. D) 0.750

Answer:  B

Difficulty:  Moderate

Topic:  Continuous Random Variables

AACSB:  Analytic Skills

Course LO:  Explain the characteristics and applications of continuous probability distributions

 

99) Given that Z is a standard normal random variable, P(-1.2 ≤ Z ≤ 1.5) is:

1. A) 0.8181
2. B) 0.4772
3. C) 0.3849
4. D) 0.5228

Answer:  A

Difficulty:  Moderate

Topic:  The Normal Distribution

AACSB:  Analytic Skills

Course LO:  Explain the characteristics and applications of continuous probability distributions

 

100) If Z is a standard normal random variable, the area between Z = 0.0 and Z =1.20 is 0.3849, while the area between Z = 0.0 and Z = 1.40 is 0.4192. What is the area between Z = -1.20 and Z = 1.40?

1. A) 0.8041
2. B) 0.0808
3. C) 0.1151
4. D) 0.0343

Answer:  A

Difficulty:  Moderate

Topic:  The Normal Distribution

AACSB:  Analytic Skills

Course LO:  Explain the characteristics and applications of continuous probability distributions

 

101) Given that Z is a standard normal variable, the value z1 for which P(Z ≤ z1) = 0.242 is:

1. A) 0.70
2. B) 0.65
3. C) -0.70
4. D) -0.65

Answer:  C

Difficulty:  Moderate

Topic:  The Normal Distribution

AACSB:  Analytic Skills

Course LO:  Explain the characteristics and applications of continuous probability distributions

 

102) The area to the left of the mean in any normal distribution is equal to:

1. A) the median.
2. B) the standard deviation.
3. C) 1.0
4. D) 0.5

Answer:  D

Difficulty:  Moderate

Topic:  The Normal Distribution

AACSB:  Analytic Skills

Course LO:  Explain the characteristics and applications of continuous probability distributions

 

103) Suppose X is a normal random variable with mean of 70 and standard deviation of 4. The Z-score was calculated for a number, and it was 2.85. What is X?

58. A) 58.6
59. B) 81.4
60. C) 65.8
61. D) 75.7

Answer:  B

Difficulty:  Moderate

Topic:  The Normal Distribution

AACSB:  Analytic Skills

Course LO:  Explain the characteristics and applications of continuous probability distributions

 

104) If Z is a standard normal random variable, then P(-1.25 ≤ Z ≤ -0.75) is:

1. A) 0.6678
2. B) 0.1056
3. C) 0.2266
4. D) 0.1210

Answer:  D

Difficulty:  Moderate

Topic:  The Normal Distribution

AACSB:  Analytic Skills

Course LO:  Explain the characteristics and applications of continuous probability distributions

 

105) The normal distribution is an example of a(n):

1. A) discrete distribution.
2. B) continuous distribution.
3. C) binomial distribution.
4. D) exponential distribution.

Answer:  B

Difficulty:  Moderate

Topic:  The Normal Distribution

AACSB:  Reflective Thinking Skills

Course LO:  Explain the characteristics and applications of continuous probability distributions

 

THE NEXT QUESTIONS ARE BASED ON THE FOLLOWING INFORMATION:

The continuous random variable X is uniformly distributed over the interval 4 to 10.

 

106) What is the mean of this distribution?

1. A) 4
2. B) 5
3. C) 6
4. D) 7

Answer:  D

Difficulty:  Moderate

Topic:  Continuous Random Variables

AACSB:  Analytic Skills

Course LO:  Explain the characteristics and applications of continuous probability distributions

 

107) What is the standard deviation of this distribution?

1. A) 1.732
2. B) 3.162
3. C) 2.646
4. D) 2.449

Answer:  A

Difficulty:  Moderate

Topic:  Continuous Random Variables

AACSB:  Analytic Skills

Course LO:  Explain the characteristics and applications of continuous probability distributions

 

108) What is P(6 ≤ X ≤ 8)?

1. A) 0.167
2. B) 0.333
3. C) 0.567
4. D) 0.833

Answer:  B

Difficulty:  Moderate

Topic:  Continuous Random Variables

AACSB:  Analytic Skills

Course LO:  Explain the characteristics and applications of continuous probability distributions

 

109) What is P(5 ≤ X ≤ 11)?

1. A) 0.167
2. B) 0.833
3. C) 1.000
4. D) 0.000

Answer:  B

Difficulty:  Moderate

Topic:  Continuous Random Variables

AACSB:  Analytic Skills

Course LO:  Explain the characteristics and applications of continuous probability distributions

 

110) The distribution that has been found to be particularly useful for waiting-line or queuing problems is referred to as the:

1. A) exponential distribution.
2. B) hypergeometric distribution.
3. C) marginal distribution.
4. D) standard normal distribution.

Answer:  A

Difficulty:  Moderate

Topic:  The Exponential Distribution

AACSB:  Reflective Thinking Skills

Course LO:  Explain the characteristics and applications of continuous probability distributions

 

111) Which type of random variables are used to model market values of various stock prices, production and sales patterns, and studies of import and export behavior?

1. A) consistent
2. B) marginal
3. C) hypergeometric
4. D) jointly distributed

Answer:  D

Difficulty:  Moderate

Topic:  Jointly Distributed Continuous Random Variables

AACSB:  Reflective Thinking Skills

Course LO:  Explain the characteristics and applications of continuous probability distributions

 

112) The combinations of continuous random variables whose development is based on operation with expected values and does not depend on the particular probability distribution are called:

1. A) marginal combinations.
2. B) frequent combinations.
3. C) linear combinations.
4. D) disjointed combinations.

Answer:  C

Difficulty:  Moderate

Topic:  Jointly Distributed Continuous Random Variables

AACSB:  Reflective Thinking Skills

Course LO:  Explain the characteristics and applications of continuous probability distributions

 

113) The term used by fund managers to describe the relationships between two stock prices is:

1. A) speculating.
2. B) hedging.
3. C) investing.
4. D) betting.

Answer:  B

Difficulty:  Moderate

Topic:  Jointly Distributed Continuous Random Variables

AACSB:  Reflective Thinking Skills

Course LO:  Explain the characteristics and applications of continuous probability distributions

 

114) One must use caution concerning finance models in that continuous clear observation and thinking cannot be replaced by models developed from:

1. A) foreign markets.
2. B) futures.
3. C) past events.
4. D) human error.

Answer:  C

Difficulty:  Moderate

Topic:  Jointly Distributed Continuous Random Variables

AACSB:  Reflective Thinking Skills

Course LO:  Explain the characteristics and applications of continuous probability distributions

 

115) A continuous uniform random variable has a constant probability density function everywhere within the range of values the random variable can take.

Answer:  TRUE

Difficulty:  Moderate

Topic:  Continuous Random Variables

AACSB:  Reflective Thinking Skills

Course LO:  Explain the characteristics and applications of continuous probability distributions

 

116) Many economic and business measures such as sales, investment, consumption, costs, and revenues can be represented by continuous random variables.

Answer:  TRUE

Difficulty:  Easy

Topic:  Continuous Random Variables

AACSB:  Reflective Thinking Skills

Course LO:  Explain the characteristics and applications of continuous probability distributions

 

117) The cumulative distribution function can be illustrated by using a simple probability structure.

Answer:  TRUE

Difficulty:  Easy

Topic:  Continuous Random Variables

AACSB:  Reflective Thinking Skills

Course LO:  Explain the characteristics and applications of continuous probability distributions

 

118) The probability that a random variable lies between a pair of values is the area under the probability density function to the left of the two values.

Answer:  FALSE

Difficulty:  Moderate

Topic:  Continuous Random Variables

AACSB:  Reflective Thinking Skills

Course LO:  Explain the characteristics and applications of continuous probability distributions

 

119) The mean of a probability distribution provides a measure of the center of the distribution.

Answer:  TRUE

Difficulty:  Moderate

Topic:  Expectations for Continuous Random Variables

AACSB:  Reflective Thinking Skills

Course LO:  Explain the characteristics and applications of continuous probability distributions

 

120) The variance of a probability distribution provides a measure of the average spread of a distribution.

Answer:  FALSE

Difficulty:  Moderate

Topic:  Expectations for Continuous Random Variables

AACSB:  Reflective Thinking Skills

Course LO:  Explain the characteristics and applications of continuous probability distributions

 

121) Although the binomial distribution is discrete and the normal distribution is continuous, the normal distribution is a good approximation for the binomial whenever nP(1 – P) > 9 where n = number of trials, and P = the probability of success in any given trial.

Answer:  TRUE

Difficulty:  Moderate

Topic:  Normal Distribution Approximation for Binomial Distribution

AACSB:  Analytic Skills

Course LO:  Explain the characteristics and applications of continuous probability distributions

 

122) The total area under the curve of the probability density function for a continuous random variable depends on the shape of the probability distribution of the random variable.

Answer:  FALSE

Difficulty:  Moderate

Topic:  Continuous Random Variables

AACSB:  Reflective Thinking Skills

Course LO:  Explain the characteristics and applications of continuous probability distributions

 

123) In any normal distribution, the mean, median, mode, and standard deviation are all at the same position on the horizontal axis.

Answer:  FALSE

Difficulty:  Moderate

Topic:  The Normal Distribution

AACSB:  Reflective Thinking Skills

Course LO:  Explain the characteristics and applications of continuous probability distributions

 

124) Any set of normally distributed data can be transformed to a standardized form.

Answer:  TRUE

Difficulty:  Moderate

Topic:  The Normal Distribution

AACSB:  Reflective Thinking Skills

Course LO:  Explain the characteristics and applications of continuous probability distributions

 

125) In the normal distribution, the curve approaches, but never intercepts the horizontal axis either to the left or right.

Answer:  TRUE

Difficulty:  Moderate

Topic:  The Normal Distribution

AACSB:  Reflective Thinking Skills

Course LO:  Explain the characteristics and applications of continuous probability distributions

 

126) The shape of the normal probability distribution is determined by the population standard deviation σ. Small values of σ reduce the height of the curve and increase the spread; large values of σ increase the height of the curve and reduce the spread.

Answer:  FALSE

Difficulty:  Moderate

Topic:  The Normal Distribution

AACSB:  Analytic Skills

Course LO:  Explain the characteristics and applications of continuous probability distributions

 

127) The standard normal distribution is the most well-known discrete distribution in statistics.

Answer:  FALSE

Difficulty:  Moderate

Topic:  The Normal Distribution

AACSB:  Reflective Thinking Skills

Course LO:  Explain the characteristics and applications of continuous probability distributions

 

128) A continuous random variable X is normally distributed with a mean of 1200 and a standard deviation of 150. Given that X = 1410, its corresponding Z-score is 1.40.

Answer:  TRUE

Difficulty:  Moderate

Topic:  The Normal Distribution

AACSB:  Analytic Skills

Course LO:  Explain the characteristics and applications of continuous probability distributions

 

129) For the uniform probability distribution, the mean and standard deviation can be calculated by knowing the maximum and minimum values of the random variable.

Answer:  TRUE

Difficulty:  Moderate

Topic:  Continuous Random Variables

AACSB:  Reflective Thinking Skills

Course LO:  Explain the characteristics and applications of continuous probability distributions

 

130) In the normal distribution, the total area beneath the curve represents the probability for all possible outcomes for a given event.

Answer:  TRUE

Difficulty:  Moderate

Topic:  The Normal Distribution

AACSB:  Reflective Thinking Skills

Course LO:  Explain the characteristics and applications of continuous probability distributions

 

131) If the random variable Z follows a standard normal distribution, then, σz = .

Answer:  TRUE

Difficulty:  Moderate

Topic:  The Normal Distribution

AACSB:  Reflective Thinking Skills

Course LO:  Explain the characteristics and applications of continuous probability distributions

 

132) If the random variable Y = a + bX, then  = .

Answer:  FALSE

Difficulty:  Moderate

Topic:  Expectations for Continuous Random Variables

AACSB:  Reflective Thinking Skills

Course LO:  Explain the characteristics and applications of continuous probability distributions

 

133) The total area under the curve of the probability density function of any normal distribution is always 1.0.

Answer:  TRUE

Difficulty:  Easy

Topic:  The Normal Distribution

AACSB:  Reflective Thinking Skills

Course LO:  Explain the characteristics and applications of continuous probability distributions

 

134) If the random variable Z follows a standard normal distribution, then  = 1.

Answer:  TRUE

Difficulty:  Easy

Topic:  The Normal Distribution

AACSB:  Reflective Thinking Skills

Course LO:  Explain the characteristics and applications of continuous probability distributions

 

135) The normal curve gets closer and closer to the X-axis but never actually touches it.

Answer:  TRUE

Difficulty:  Moderate

Topic:  The Normal Distribution

AACSB:  Reflective Thinking Skills

Course LO:  Explain the characteristics and applications of continuous probability distributions

 

136) If the covariance of two random variables X and Y is positive, then Var(X – Y) will be larger than Var(X + Y).

Answer:  FALSE

Difficulty:  Moderate

Topic:  Jointly Distributed Continuous Random Variables

AACSB:  Analytic Skills

Course LO:  Explain the characteristics and applications of continuous probability distributions

 

137) There is not just one normal probability distribution; there is a family of distributions.

Answer:  TRUE

Difficulty:  Moderate

Topic:  The Normal Distribution

AACSB:  Reflective Thinking Skills

Course LO:  Explain the characteristics and applications of continuous probability distributions

 

138) If X is a normal random variable with mean μ = 4 and standard deviation σ = 2, and Y is a
normal random variable with mean μ = 10 and standard deviation σ = 5, then the probabilities P(X < 0) and P(Y < 0) are equal.

Answer:  TRUE

Difficulty:  Moderate

Topic:  The Normal Distribution

AACSB:  Analytic Skills

Course LO:  Explain the characteristics and applications of continuous probability distributions

 

139) The probability density function for the exponential distribution is bell-shaped and symmetrical around the mean λ.

Answer:  FALSE

Difficulty:  Moderate

Topic:  The Exponential Distribution

AACSB:  Reflective Thinking Skills

Course LO:  Explain the characteristics and applications of continuous probability distributions

 

140) If X is a normal random variable with mean of 2 and standard deviation of 5, then P(X < 3) = P(X > 7).

Answer:  FALSE

Difficulty:  Moderate

Topic:  The Normal Distribution

AACSB:  Analytic Skills

Course LO:  Explain the characteristics and applications of continuous probability distributions

 

141) For a normal distribution, practically all the area under the normal curve is within plus or minus three standard deviations from the mean.

Answer:  TRUE

Difficulty:  Moderate

Topic:  The Normal Distribution

AACSB:  Reflective Thinking Skills

Course LO:  Explain the characteristics and applications of continuous probability distributions

 

142) Given a normal random variable X with mean of 70 and standard deviation of 12, the value of the standard normal random variable Z associated with X = 82 is larger than zero.

Answer:  TRUE

Difficulty:  Moderate

Topic:  The Normal Distribution

AACSB:  Analytic Skills

Course LO:  Explain the characteristics and applications of continuous probability distributions

 

143) The standardized normal distribution has a mean = 0 and a standard deviation = 10.

Answer:  FALSE

Difficulty:  Moderate

Topic:  The Normal Distribution

AACSB:  Analytic Skills

Course LO:  Explain the characteristics and applications of continuous probability distributions

 

144) If the random variable Y = a + bX, then μY = a + bμX.

Answer:  TRUE

Difficulty:  Moderate

Topic:  Expectations for Continuous Random Variables

AACSB:  Reflective Thinking Skills

Course LO:  Explain the characteristics and applications of continuous probability distributions

 

145) A normal probability plot may be used to assess the assumption of normality for a particular set of data values.

Answer:  TRUE

Difficulty:  Moderate

Topic:  The Normal Distribution

AACSB:  Reflective Thinking Skills

Course LO:  Explain the characteristics and applications of continuous probability distributions

 

146) If the random variable X follows a binomial distribution with parameters n and P, then when using the normal distribution to approximate the distribution of X, we should use nP for the mean and nP(1-P) for the standard deviation.

Answer:  FALSE

Difficulty:  Moderate

Topic:  Normal Distribution Approximation for Binomial Distribution

AACSB:  Reflective Thinking Skills

Course LO:  Explain the characteristics and applications of continuous probability distributions

 

147) Any set of normally distributed data can always be transformed into a standard normal distribution with a mean = 0 and a standard deviation = 1.

Answer:  TRUE

Difficulty:  Moderate

Topic:  The Normal Distribution

AACSB:  Analytic Skills

Course LO:  Explain the characteristics and applications of continuous probability distributions

 

148) Given that Z is a standard normal random variable, a negative value of Z indicates that the standard deviation of z is negative.

Answer:  FALSE

Difficulty:  Moderate

Topic:  The Normal Distribution

AACSB:  Analytic Skills

Course LO:  Explain the characteristics and applications of continuous probability distributions

 

149) The normal probability distribution provides a very close approximation to the binomial probability distribution if np(1 – p) > 5, where n is the number of trials and p is the probability of success in any trial.

Answer:  TRUE

Difficulty:  Moderate

Topic:  Normal Distribution Approximation for Binomial Distribution

AACSB:  Analytic Skills

Course LO:  Explain the characteristics and applications of continuous probability distributions

 

150) Given a normal random variable X with mean μ and standard deviation σ, the standard normal random variable associated with x is Z = (X – μ)/σ.

Answer:  TRUE

Difficulty:  Moderate

Topic:  The Normal Distribution

AACSB:  Reflective Thinking Skills

Course LO:  Explain the characteristics and applications of continuous probability distributions

 

151) If a data set is approximately normally distributed, then its normal probability plot will be S-shaped.

Answer:  FALSE

Difficulty:  Moderate

Topic:  The Normal Distribution

AACSB:  Reflective Thinking Skills

Course LO:  Explain the characteristics and applications of continuous probability distributions

 

152) The mean and variance of any normal distribution are always zero and one, respectively.

Answer:  FALSE

Difficulty:  Moderate

Topic:  The Normal Distribution

AACSB:  Reflective Thinking Skills

Course LO:  Explain the characteristics and applications of continuous probability distributions

 

153) The proportion of the total area under the normal curve that lies within ± one standard deviation of the mean is approximately 0.75.

Answer:  FALSE

Difficulty:  Moderate

Topic:  The Normal Distribution

AACSB:  Analytic Skills

Course LO:  Explain the characteristics and applications of continuous probability distributions

 

154) If the random variables X and Y are statistically independent, then their joint cumulative distribution function can be represented as the product of the marginal cumulative distribution functions of X and Y.

Answer:  TRUE

Difficulty:  Moderate

Topic:  Jointly Distributed Continuous Random Variables

AACSB:  Reflective Thinking Skills

Course LO:  Explain the characteristics and applications of continuous probability distributions

 

155) The area under a valid cumulative distribution function is equal to 1.

Answer:  FALSE

Difficulty:  Moderate

Topic:  Continuous Random Variables

AACSB:  Analytic Skills

Course LO:  Explain the characteristics and applications of continuous probability distributions

 

156) The cumulative distribution function for a random variable X, F(x0), is the area under the probability density function f(x) up to x0.

Answer:  TRUE

Difficulty:  Moderate

Topic:  Continuous Random Variables

AACSB:  Reflective Thinking Skills

Course LO:  Explain the characteristics and applications of continuous probability distributions

 

157) The mean and median are the same for a random variable that is exponentially distributed.

Answer:  FALSE

Difficulty:  Moderate

Topic:  The Exponential Distribution

AACSB:  Reflective Thinking Skills

Course LO:  Explain the characteristics and applications of continuous probability distributions

 

158) Linear functions of random variables have many applications such as in the case of car dealership sales.

Answer:  TRUE

Difficulty:  Moderate

Topic:  Expectations for Continuous Random Variables

AACSB:  Reflective Thinking Skills

Course LO:  Explain the characteristics and applications of continuous probability distributions

 

159) The normal probability distribution is the continuous probability distribution used least often for economics and business applications.

Answer:  FALSE

Difficulty:  Moderate

Topic:  The Normal Distribution

AACSB:  Reflective Thinking Skills

Course LO:  Explain the characteristics and applications of continuous probability distributions

 

160) We can obtain probabilities for any normally distributed random variable by first converting the random variable to the standard normally distributed random variable.

Answer:  TRUE

Difficulty:  Moderate

Topic:  The Normal Distribution

AACSB:  Reflective Thinking Skills

Course LO:  Explain the characteristics and applications of continuous probability distributions

 

161) Normal probability plots provide a way to test the assumption that the normal distribution is a close approximation to the actual unknown distribution that supplied the data we are analyzing.

Answer:  TRUE

Difficulty:  Moderate

Topic:  The Normal Distribution

AACSB:  Reflective Thinking Skills

Course LO:  Explain the characteristics and applications of continuous probability distributions

 

162) We can reduce the number of different statistical procedures needed to solve business problems by applying procedures based on the normal distribution to problems involving binomial and proportion random variables.

Answer:  TRUE

Difficulty:  Moderate

Topic:  Normal Distribution Approximation for Binomial Distribution

AACSB:  Reflective Thinking Skills

Course LO:  Explain the characteristics and applications of continuous probability distributions

 

163) The normal distribution is useful for waiting-line or queuing problems and service-time problems.

Answer:  FALSE

Difficulty:  Moderate

Topic:  The Normal Distribution

AACSB:  Reflective Thinking Skills

Course LO:  Explain the characteristics and applications of continuous probability distributions

 

164) In using finance models we must be aware that caution and continuous clear observation and thinking cannot be replaced by models developed from past events.

Answer:  TRUE

Difficulty:  Moderate

Topic:  Jointly Distributed Continuous Random Variables

AACSB:  Reflective Thinking Skills

Course LO:  Explain the characteristics and applications of continuous probability distributions

 

165) The normal distribution is used to approximate the binomial under certain conditions. What is the best way to approximate the binomial using the normal?

Answer:  When the number of trials n is large enough such that np(1 – p) > 5, where p is the probability of success in any trial, the binomial distribution often looks like a bell-shaped curve and it is approximated by a normal distribution with the same mean and variance. In this case, the binomial probabilities can be approximated by the probabilities under the normal curve. The best way to approximate a discrete random variable, such as the binomial, by a continuous random variable, such as the normal. The normal probabilities are calculated as Z =

Difficulty:  Moderate

Topic:  Normal Distribution Approximation for Binomial Distribution

AACSB:  Analytic Skills

Course LO:  Explain the characteristics and applications of continuous probability distributions

 

166) Suppose that 24% of all sales in a grocery store are for amounts greater than $100. In a random sample of 50 invoices, what is the probability that more than ten of the invoices are for over $100? Use the normal approximation for the binomial distribution.

Answer:  P = 0.24, n = 50, μ =E(X) = nP = 12, σ2 = Var(X) = nP(1 – P) = 9.12, σ = 3.02

Without continuity correction P(X > 10) = P(Z > -0.66) = 0.7454.

Difficulty:  Moderate

Topic:  Normal Distribution Approximation for Binomial Distribution

AACSB:  Analytic Skills

Course LO:  Explain the characteristics and applications of continuous probability distributions

 

167) Investment A has an expected return of 10% with a standard deviation of 3.5%. Investment B has an expected return of 6% with a standard deviation of 1.2%. If you invest equally in both investments, what is the expected return and standard deviation of your portfolio? What assumptions have you made?

Answer:  E(A + B) = 0.10 + 0.06 = 0.16

Assume the rates of return are independent, Var(A + B) = Var(A) + Var(B) = 13.69. Hence, σ of (A + B) = 3.7

Difficulty:  Moderate

Topic:  Jointly Distributed Continuous Random Variables

AACSB:  Analytic Skills

Course LO:  Explain the characteristics and applications of continuous probability distributions

 

THE NEXT QUESTIONS ARE BASED ON THE FOLLOWING INFORMATION:

The amount of time you have to wait at a dentist’s office before you are called in is uniformly distributed between zero and twenty minutes.

 

168) What is the probability that you have to wait more than 8 minutes?

Answer:  P(X > 8) = (20 – 8)/(20 – 0) = 12/20 = 0.60

Difficulty:  Moderate

Topic:  Continuous Random Variables

AACSB:  Analytic Skills

Course LO:  Explain the characteristics and applications of continuous probability distributions

 

169) What is the probability that you have to wait between 10 and 15 minutes?

Answer:  P(10 < X < 15) = (15 – 10)/(20 – 0) = 5/20 = 0.25

Difficulty:  Moderate

Topic:  Continuous Random Variables

AACSB:  Analytic Skills

Course LO:  Explain the characteristics and applications of continuous probability distributions

 

170) Seventy percent of the time, you will be called in before you have to wait how long?

Answer:  The range is a total of 20 minutes. 70% of the time, you should be called in before you wait 14 minutes.

Difficulty:  Moderate

Topic:  Continuous Random Variables

AACSB:  Analytic Skills

Course LO:  Explain the characteristics and applications of continuous probability distributions

 

THE NEXT QUESTIONS ARE BASED ON THE FOLLOWING INFORMATION:

The average amount of time between a score by either team in college soccer games is 15.2 minutes. Suppose that the time between scores follows an exponential distribution.

 

171) What is the probability that a soccer game goes for 45 minutes without either team scoring?

Answer:  E(T) =1/λ = 15.2, then, λ = 0.0658, and P(T > 45) = e-λ45 = e-2.961 = 0.0518

Difficulty:  Moderate

Topic:  The Exponential Distribution

AACSB:  Analytic Skills

Course LO:  Explain the characteristics and applications of continuous probability distributions

 

172) The length of time it takes to fill an order at a local sandwich shop is normally distributed with a mean of 4.1 minutes and a standard deviation of 1.3 minutes. If the sandwich shop employees make $6.00 an hour, what is the mean and standard deviation for the labor costs per sandwich?

Answer:  μX = 4.1 and  = 1.69. Labor cost per minute = $0.10, Y = 0.10X.

μY = 0.10 μX = (0.10)(4.1) = $0.41, = (0.10)2  = 0.0169. Hence, σY = 0.13.

Difficulty:  Moderate

Topic:  The Normal Distribution

AACSB:  Analytic Skills

Course LO:  Explain the characteristics and applications of continuous probability distributions

 

173) You are the owner of a small casino in Las Vegas. You want to reward the high-rollers who come to your casino. You want to give free accommodations to no more than 10% of your patrons. Suppose that the mean amount wagered by all patrons is $287, with a standard deviation of $15. You should give free accommodations to those individuals who wager over how much money?

Answer:  P(X > k) = 0.10 ⇒ P[Z > (k-287) / 15] = 0.10 ⇒ (k – 287) / 15 = 1.28 ⇒ k = $306.20

Difficulty:  Moderate

Topic:  The Normal Distribution

AACSB:  Analytic Skills

Course LO:  Explain the characteristics and applications of continuous probability distributions

 

174) You are in charge of arranging the catering for a company meeting. Your company is responsible for paying for all meals ordered, so you don’t want to order too many. Suppose that the expected number of people for the meeting is 84, with a standard deviation of 4 people. What is the fewest number of meals should you order so that the probability of having more people than meals is 5%?

Answer:  P(X > k) = 0.05 ⇒ P[Z > (k – 84) / 4] = 0.05 ⇒ (k – 84) / 4 = 1.645 ⇒ k = 90.58 ≈ 91 meals

Difficulty:  Moderate

Topic:  The Normal Distribution

AACSB:  Analytic Skills

Course LO:  Explain the characteristics and applications of continuous probability distributions

 

175) It has been found that 62.1% of all unsolicited third class mail delivered to households goes unread. If, over the course of a month, a household receives 150 pieces of unsolicited mail, what is the probability that the household discards more than 80 pieces of the mail without reading it? Use the normal approximation for the binomial distribution.

Answer:  P = 0.621, n = 150, μ = E(X) = 93.15, σ2 =Var(X) = nP(1 – P) = 35.3039, σ= 5.942

P(X > 80) = P(Z > -2.21) = 0.9864.

Difficulty:  Moderate

Topic:  The Normal Distribution

AACSB:  Analytic Skills

Course LO:  Explain the characteristics and applications of continuous probability distributions

 

THE NEXT QUESTIONS ARE BASED ON THE FOLLOWING INFORMATION:

Let the random variable Z follow a standard normal distribution.

 

176) What is P(Z > 0.29)?

Answer:  0.3859

Difficulty:  Moderate

Topic:  The Normal Distribution

AACSB:  Analytic Skills

Course LO:  Explain the characteristics and applications of continuous probability distributions

 

177) What is P(Z < 1.23)?

Answer:  0.8907

Difficulty:  Moderate

Topic:  The Normal Distribution

AACSB:  Analytic Skills

Course LO:  Explain the characteristics and applications of continuous probability distributions

 

178) What is P(Z > -0.52)?

Answer:  0.6985

Difficulty:  Moderate

Topic:  The Normal Distribution

AACSB:  Analytic Skills

Course LO:  Explain the characteristics and applications of continuous probability distributions

 

179) What is P(-0.44 < Z < 1.2)?

Answer:  0.5549

Difficulty:  Moderate

Topic:  The Normal Distribution

AACSB:  Analytic Skills

Course LO:  Explain the characteristics and applications of continuous probability distributions

 

180) As manager of a pizza shop, you are responsible for placing the food orders. You currently have enough anchovies for 8 pizzas. You expect to have orders for 60 pizzas tonight. If 8% of all pizzas are ordered with anchovies, what is the probability that you run out of anchovies before the evening is over? Use the normal approximation for the binomial.

Answer:  P = 0.08, n = 60, μ = E(X) = 4.8, σ2 = Var(X) = nP(1 – P) = 4.416, σ= 2.1

P(X > 8) = P(Z > 1.52) = 0.0643

Difficulty:  Moderate

Topic:  The Normal Distribution

AACSB:  Analytic Skills

Course LO:  Explain the characteristics and applications of continuous probability distributions

 

THE NEXT QUESTIONS ARE BASED ON THE FOLLOWING INFORMATION:

Let the random variable Z follow a standard normal distribution.

 

181) Find the value k such that P(Z > k) = 0.83

Answer:  k = -0.95

Difficulty:  Moderate

Topic:  The Normal Distribution

AACSB:  Analytic Skills

Course LO:  Explain the characteristics and applications of continuous probability distributions

 

182) Find the value k such that P(Z > k) = 0.43

Answer:  k = 0.18

Difficulty:  Moderate

Topic:  The Normal Distribution

AACSB:  Analytic Skills

Course LO:  Explain the characteristics and applications of continuous probability distributions

 

183) Find the value k such that P(0 < Z < k) = 0.35

Answer:  k = 1.04

Difficulty:  Moderate

Topic:  The Normal Distribution

AACSB:  Analytic Skills

Course LO:  Explain the characteristics and applications of continuous probability distributions

 

184) Find the value k such that P(-0.71 < Z < k) ≈ 0.67

Answer:  k = 1.33

Difficulty:  Moderate

Topic:  The Normal Distribution

AACSB:  Analytic Skills

Course LO:  Explain the characteristics and applications of continuous probability distributions

 

185) The time it takes to assemble an electronic component is normally distributed with a mean of 17.2 minutes and a standard deviation of 3.1 minutes. The probability is 90% that it will take at least how long to assemble a component?

Answer:  P(X > k) = 0.90 ⇒ P[Z > (k – 17.2)/3.1] = 0.90 (k – 17.2) /3.1 = -1.28, ⇒ k = 13.23 minutes

Difficulty:  Moderate

Topic:  The Normal Distribution

AACSB:  Analytic Skills

Course LO:  Explain the characteristics and applications of continuous probability distributions

 

THE NEXT QUESTIONS ARE BASED ON THE FOLLOWING INFORMATION:

The stamping machine on a production line periodically is taken off-line for maintenance. Assume that the amount of time the machine is off-line is uniformly distributed between 15 and 30 minutes.

 

186) What is the probability that the machine is off-line for more than 18 minutes?

Answer:  18 to 30 minutes represent 80% of the distance between 15 and 30 minutes.
Hence, P(X > 18) = 0.80.

Difficulty:  Moderate

Topic:  Continuous Random Variables

AACSB:  Analytic Skills

Course LO:  Explain the characteristics and applications of continuous probability distributions

 

187) What is the probability that the machine is off-line between 21 and 27 minutes?

Answer:  21 to 27 minutes represents 40% of the distance between 15 and 30 minutes.
Hence, P(21 ≤ X ≤27) = 0.40.

Difficulty:  Moderate

Topic:  Continuous Random Variables

AACSB:  Analytic Skills

Course LO:  Explain the characteristics and applications of continuous probability distributions

 

188) In a recent survey of high school students, it was found that the average amount of money spent on entertainment each week was normally distributed with a mean of $52.30. Suppose you are told that there is an 80% probability that a randomly-selected student spends somewhere between $49.74 and $54.86. What is the standard deviation of the amount of money spent by high school students monthly?

Answer:  P(49.74 < X < 54.86) = P[(49.74 – 52.30)/ σ < Z < (54.86 – 52.30)/σ] = 0.80

⇒ P  = 0.80. Hence, P(Z < 2.56/σ) = 0.90

⇒ 2.56/ σ = 1.28 ⇒ σ = 2.0

Difficulty:  Moderate

Topic:  The Normal Distribution

AACSB:  Analytic Skills

Course LO:  Explain the characteristics and applications of continuous probability distributions

 

THE NEXT QUESTIONS ARE BASED ON THE FOLLOWING INFORMATION:

A wire-spinning machine will spin, on average, 12.3 miles before needing maintenance. Assume the time between maintenance is exponentially distributed.

 

189) What is the probability that a spinning machine just placed back in service will need maintenance before it produces 4 miles of wire?

Answer:  E(X) = 1/λ =12.3, then λ= 0.0813, and P(X < 4) = 1 – e-4λ = 1 – e-0.3252 = 0.2776.

Difficulty:  Moderate

Topic:  The Exponential Distribution

AACSB:  Analytic Skills

Course LO:  Explain the characteristics and applications of continuous probability distributions

 

190) What is the median amount of time before the machine needs servicing?

Answer:  Median k such that 1 – e-kλ = 1 – e-0.0813k = 0.50 ⇒ k = 8.53 miles.

Difficulty:  Moderate

Topic:  The Exponential Distribution

AACSB:  Analytic Skills

Course LO:  Explain the characteristics and applications of continuous probability distributions

 

191) You are the Webmaster for your firm’s Website. From your records, you know that the probability that a visitor will buy something from your firm is 0.23. If the number of visitors in one day is 952, what is the probability that less than 200 of them will buy something from your firm? Use the normal approximation for the binomial.

Answer:  n = 952, P = 0.23, μ =E(X) = 218.96, σ2 =Var(X) = nP(1 – P) = 168.5992, σ = 12.985

P(X < 200) = P(Z < -1.46) = 0.0721

Difficulty:  Moderate

Topic:  Normal Distribution Approximation for Binomial Distribution

AACSB:  Analytic Skills

Course LO:  Explain the characteristics and applications of continuous probability distributions

 

THE NEXT QUESTIONS ARE BASED ON THE FOLLOWING INFORMATION:

The life of a new type of light bulb is uniformly distributed between 1,200 and 1,600 hours.

 

192) The probability is 70% that a randomly-selected light bulb will last at least how long.

Answer:  70% of the distance from 1200 to 1600 is 280. Then, t = 1200 + 280 = 1480.

Difficulty:  Moderate

Topic:  Continuous Random Variables

AACSB:  Analytic Skills

Course LO:  Explain the characteristics and applications of continuous probability distributions

 

193) What is the probability that a randomly-selected light bulb burns out in less than 1,500 hours?

Answer:  P(X < 1500) = (1500 – 1200)/(1600 – 1200) = 300/400 = 0.75

Difficulty:  Moderate

Topic:  Continuous Random Variables

AACSB:  Analytic Skills

Course LO:  Explain the characteristics and applications of continuous probability distributions

 

194) Sales at a local plumbing wholesaler consist of both over-the-counter sales as well as deliveries. During the course of a month, over-the-counter sales have a mean of $102,972 with a standard deviation of $13,523. Over the same time period, deliveries average $242,354 with a standard deviation of $24,956. Assuming that the sales over-the-counter are independent of deliveries, what are the mean and standard deviation of the wholesaler monthly sales?

Answer:  Let X = over-the-counter sales, Let Y = deliveries, and W=Wholesaler’s monthly sales

E(W) = E(X + Y) = E(X) + E(Y) = 102972 + 242354 = $345,326

= Var(W) = Var(X + Y) = Var(X) + Var(Y) = 805,673,465, σW = $28,384

Difficulty:  Moderate

Topic:  Jointly Distributed Continuous Random Variables

AACSB:  Analytic Skills

Course LO:  Explain the characteristics and applications of continuous probability distributions

 

195) During normal business hours at a gas station, customers arrive, on average, every ten minutes. Assume that the distribution of the time between arrivals follows an exponential distribution. Suppose that a customer has just left the gas station. What is the probability that the cashier at the gas station has more than 15 minutes before the next customer arrive?

Answer:  Exponential with mean 1/λ = 10, then, λ = 0.10, and P(T > 15) = e-15λ = e-1.5 = 0.223

Difficulty:  Moderate

Topic:  The Exponential Distribution

AACSB:  Analytic Skills

Course LO:  Explain the characteristics and applications of continuous probability distributions

 

196) The number of viewers ordering a particular pay-per-view program is normally distributed. 20% of the time, fewer than 20,000 people order the program. Only ten percent of the time more than 28,000 people order the program. What is the mean and standard deviation of the number of people ordering the program?

Answer:  P(X < 20,000) = 0.2, and P(X > 28,000) = 0.10

P[Z < (20,000 – k)/m] = 0.2, and P[Z > (28,000 – k)/m] = 0.10. Then,

(20,000 – k)/m) = -0.84 and (28,000 – k)/m) = 1.28.

We have two equations in two unknowns. Solving simultaneously: 2.12 m = 8,000 or m = 3,774. If m = 3774, then k = 23,170. Hence, Mean = 23,170, standard deviation = 3,774.

Difficulty:  Moderate

Topic:  The Normal Distribution

AACSB:  Analytic Skills

Course LO:  Explain the characteristics and applications of continuous probability distributions

 

THE NEXT QUESTIONS ARE BASED ON THE FOLLOWING INFORMATION:

Let the random variable X follow a normal distribution with mean μ = 48 and variance σ2 = 60.84.

 

197) Find the probability that X is greater than 58.

Answer:  P(X > 58) = P( Z > 1.28) = 0.50 – 0.3997 = 0.1003

Difficulty:  Moderate

Topic:  The Normal Distribution

AACSB:  Analytic Skills

Course LO:  Explain the characteristics and applications of continuous probability distributions

 

198) Find the probability that X is greater than 36 and less than 60.

Answer:  P(36 < X < 60) = P(-1.54 < Z < 1.54) = 0.4382 + 0.4382 = 0.8764

Difficulty:  Moderate

Topic:  The Normal Distribution

AACSB:  Analytic Skills

Course LO:  Explain the characteristics and applications of continuous probability distributions

 

199) Find the probability that X is less than 52.

Answer:  P(X < 52) = P(Z < 0.51) = 0.195 + 0.50 = 0.695

Difficulty:  Moderate

Topic:  The Normal Distribution

AACSB:  Analytic Skills

Course LO:  Explain the characteristics and applications of continuous probability distributions

 

200) The probability is 0.2 that X is greater than what number?

Answer:  P(X > a) = 0.20 ⇒ P[Z > (a – 48) / 7.8] = 0.20 ⇒ (a – 48) / 7.8 = 0.84 ⇒ a = 54.552

Difficulty:  Moderate

Topic:  The Normal Distribution

AACSB:  Analytic Skills

Course LO:  Explain the characteristics and applications of continuous probability distributions

 

201) The probability is approximately 0.05 that X is in the symmetric interval about the mean between which two numbers?

Answer:  P(a < X < b) = 0.05 ⇒ P[(a – 48) / 7.8 < Z < (b – 48) / 7.8] = 0.05

⇒ (a – 48) / 7.8 = -0.06 and (b – 48) / 7.8 = 0.06

⇒ a = 47.532 and b = 48.468

Difficulty:  Moderate

Topic:  The Normal Distribution

AACSB:  Analytic Skills

Course LO:  Explain the characteristics and applications of continuous probability distributions

 

202) The binomial distribution and the normal distribution are similar in a number of ways, although they are different distributions. What are the basic differences between the two distributions?

Answer:  The binomial distribution is a discrete probability distribution. Outcomes are
integers 1, 2, 3,…n where n is the number of trials for the binomial random variable. The normal distribution is a continuous probability distribution with a bell-shaped curve describing the shape of the distribution. A normal random variable can take on an infinite number of values within an interval.

Difficulty:  Moderate

Topic:  Normal Distribution Approximation for Binomial Distribution

AACSB:  Reflective Thinking Skills

Course LO:  Explain the characteristics and applications of continuous probability distributions

 

THE NEXT QUESTIONS ARE BASED ON THE FOLLOWING INFORMATION:

A professor sees students during regular office hours. Times spent with students follow an exponential distribution with mean of 12 minutes.

 

203) Find the probability that a given student spends less than 15 minutes with the professor.

Answer:  P(X < 15) = 1 – e-(1/12)15 = 1 – e-1.25 = 0.7135

Difficulty:  Moderate

Topic:  The Exponential Distribution

AACSB:  Analytic Skills

Course LO:  Explain the characteristics and applications of continuous probability distributions

 

204) Find the probability that a given student spends more than 8 minutes with the professor.

Answer:  P(X > 8) = 1 – [1 – e-(1/12)8] = e-0.667 = 0.5132

Difficulty:  Moderate

Topic:  The Exponential Distribution

AACSB:  Analytic Skills

Course LO:  Explain the characteristics and applications of continuous probability distributions

 

205) Find the probability that a given student spends between 12 and 15 minutes with the professor.

Answer:  P(12 < X < 15) = [(1 – e-(1/12)15 – (1 – e-(1/12)12)] = e-1.0 – e-1.25 = 0.0814

Difficulty:  Moderate

Topic:  The Exponential Distribution

AACSB:  Analytic Skills

Course LO:  Explain the characteristics and applications of continuous probability distributions

 

206) The total cost for a production process is equal to $1,200 plus 2.5 times the number of units produced. The mean and variance for the number of units produced are 520 and 840, respectively. Find the mean and variance of the total cost.

Answer:  Let X = number of units produced, and T = total cost for the production process.

Since T = 1200 + 2.5X, μX = 520 and = 840, then

μT = 1200 + 2.5μX = 1200 + (2.5)(520) = 2500, and  = (2.5)2  = (6.25)(840) = 5250

Difficulty:  Moderate

Topic:  Expectations for Continuous Random Variables

AACSB:  Analytic Skills

Course LO:  Explain the characteristics and applications of continuous probability distributions

 

THE NEXT QUESTIONS ARE BASED ON THE FOLLOWING INFORMATION:

A random variable X is normally distributed with mean of 50 and variance of 50, and a random variable Y is normally distributed with mean of 100 and variance of 200.

 

207) Given the random variables X and Y have a correlation coefficient equal to 0.50, find the mean and variance of the random variable W = 4X+3Y.

Answer:  μX = 50,  = 50, μY = 100,  = 200, Corr(X, Y) = 0.50

μW = 4μX + 3μY = (4)(50) + (3)(100) = 500

= (4)2  + (3)2  + 2(4)(3)Corr(X, Y)σX σY

= (16)(50) + (9)(200) + (24)(0.50)(7.071)(14.142) = 3,799.977

Difficulty:  Moderate

Topic:  Jointly Distributed Continuous Random Variables

AACSB:  Analytic Skills

Course LO:  Explain the characteristics and applications of continuous probability distributions

 

208) Given the random variables X and Y have a correlation coefficient equal to 0.50, find the mean and variance of the random variable W = 4X – 3Y.

Answer:  μX = 50,  = 50, μY = 100,  = 200, Corr(X, Y) = 0.50

μW = 4μX – 3μY = (4)(50) – (3)(100) = -100

= (4)2  + (-3)2  + 2(4)(-3)Corr(X, Y)σX σY

= (16)(50) + (9)(200) – (24)(0.50)(7.071)(14.142) = 1,400.023

Difficulty:  Moderate

Topic:  Jointly Distributed Continuous Random Variables

AACSB:  Analytic Skills

Course LO:  Explain the characteristics and applications of continuous probability distributions

 

209) Given the random variables X and Y have a correlation coefficient equal to -0.50, find the mean and variance of the random variable W = 4X + 3Y.

Answer:  μX = 50,  = 50, μY = 100,  = 200, Corr(X, Y) = 0.50

μW = 4μX + 3μY = (4)(50) + (3)(100) = 500

= (4)2  + (3)2  + 2(4)(3)Corr(X, Y)σX σY

= (16)(50) + (9)(200) + (24)(-0.50)(7.071)(14.142) = 1,400.023

Difficulty:  Moderate

Topic:  Jointly Distributed Continuous Random Variables

AACSB:  Analytic Skills

Course LO:  Explain the characteristics and applications of continuous probability distributions

 

210) Given the random variables X and Y have a correlation coefficient equal to -0.50, find the mean and variance of the random variable W = 4X – 3Y.

Answer:  μX = 50,  = 50, μY = 100,  = 200, Corr(X, Y) = 0.50

μW = 4μX – 3μY = (4)(50) – (3)(100) = -100

= (4)2  + (-3)2  + 2(4)(-3)Corr(X, Y)σX σY

= (16)(50) + (9)(200) – (24)(-0.50)(7.071)(14.142) = 3,799.977

Difficulty:  Moderate

Topic:  Jointly Distributed Continuous Random Variables

AACSB:  Analytic Skills

Course LO:  Explain the characteristics and applications of continuous probability distributions

 

211) The profit for a production process is equal to $7,200 minus 2.8 times the number of units produced. The mean and variance for the number of units produced are 1,100 and 800, respectively. Find the mean and variance of the profit.

Answer:  Let X = number of units produced, and P = profit for the production process.

Since P = 7200 – 2.8X, μX = 1100 and  = 800, then

μP = 7200 – (2.8)μX = 7200 – (2.8)(1100) = 4120, and  = (2.8)2  = (7.84)(800) = 6272

Difficulty:  Moderate

Topic:  Expectations for Continuous Random Variables

AACSB:  Analytic Skills

Course LO:  Explain the characteristics and applications of continuous probability distributions

 

THE NEXT QUESTIONS ARE BASED ON THE FOLLOWING INFORMATION:

Consider a random sample of size n =1800 from a binomial probability distribution with P = 0.40, and X = number of successes.

 

212) Find the mean and standard deviation of the number of successes.

Answer:  Mean = E(X) = μ = nP = (1800)(0.40) = 720

Standard deviation = σ =  =  = 20.785

Difficulty:  Moderate

Topic:  Normal Distribution Approximation for Binomial Distribution

AACSB:  Analytic Skills

Course LO:  Explain the characteristics and applications of continuous probability distributions

 

213) Find the probability that the number of successes is greater than 775.

Answer:  P(X > 775 | n = 1800, P = 0.40) ≈ P(X > 775 | μ = 720, σ = 20.785)

= P(Z > 2.65)

= 0.50 – 0.4960 = 0.004

Difficulty:  Moderate

Topic:  Normal Distribution Approximation for Binomial Distribution

AACSB:  Analytic Skills

Course LO:  Explain the characteristics and applications of continuous probability distributions

 

214) Find the probability that the number of successes is less than 700.

Answer:  P(X < 700 | n = 1800, P = 0.40) ≈ P(X < 700 |μ = 720, σ = 20.785)

= P(Z < -0.96)

= 0.50 – 0.3315 = 0.1685

Difficulty:  Moderate

Topic:  Normal Distribution Approximation for Binomial Distribution

AACSB:  Analytic Skills

Course LO:  Explain the characteristics and applications of continuous probability distributions

 

215) Find the probability that the number of successes is between 680 and 750.

Answer:  P(680 < X < 750 | n = 1800, P = 0.40) ≈ P(680 < X < 750 | μ = 720, σ = 20.785)

= P(-1.92 < Z < 1.44)

= 0.4726 + 0.4251 = 0.8977

Difficulty:  Moderate

Topic:  Normal Distribution Approximation for Binomial Distribution

AACSB:  Analytic Skills

Course LO:  Explain the characteristics and applications of continuous probability distributions

 

216) With probability 0.09 the number of successes is less than how many?

Answer:  P(X < a | n = 1800, P = 0.40) ≈ P(X < a | μ = 720, σ = 20.785) = 0.09

⇒ P[Z < (a – 720) / 20.875] = 0.09

⇒ (a – 720) / 20.875 = -1.34

⇒ a = 692.02 ≈ 692

Difficulty:  Moderate

Topic:  Normal Distribution Approximation for Binomial Distribution

AACSB:  Analytic Skills

Course LO:  Explain the characteristics and applications of continuous probability distributions

 

217) With probability 0.20, the number of successes is greater than how many?

Answer:  P(X > a | n = 1800, P = 0.40) ≈ P(X > a | μ = 720, σ = 20.785) = 0.20

⇒ P[Z > (a – 720) / 20.875] = 0.20

⇒ (a – 720) / 20.875 = 0.84

⇒ a = 737.54 or 734

Difficulty:  Moderate

Topic:  Normal Distribution Approximation for Binomial Distribution

AACSB:  Analytic Skills

Course LO:  Explain the characteristics and applications of continuous probability distributions

 

218) Find the mean and standard deviation of the proportion of successes.

Answer:  Mean = μ = P = 0.40,

Standard deviation = σ =  =  = 0.01155

Difficulty:  Moderate

Topic:  Normal Distribution Approximation for Binomial Distribution

AACSB:  Analytic Skills

Course LO:  Explain the characteristics and applications of continuous probability distributions

 

219) Find the probability that the percentage of successes is greater than 0.42

Answer:  P(P > 0.42 | n = 1800, P = 0.40) ≈ P(P > 0.42 | μ= 0.40, σ= 0.01155)

= P(Z > 1.73)

= 0.50 – 0.4582 = 0.0418

Difficulty:  Moderate

Topic:  Normal Distribution Approximation for Binomial Distribution

AACSB:  Analytic Skills

Course LO:  Explain the characteristics and applications of continuous probability distributions

 

220) Find the probability that the percentage of successes is less than 0.37

Answer:  P(P < 0.37 | n = 1800, P = 0.40) ≈ P(P < 0.37 | μ = 0.40, σ = 0.01155)

= P(Z < -2.60)

= 0.50 -.4953 = 0.0047

Difficulty:  Moderate

Topic:  Normal Distribution Approximation for Binomial Distribution

AACSB:  Analytic Skills

Course LO:  Explain the characteristics and applications of continuous probability distributions

 

221) Find the probability that the percentage of successes is between 0.38 and 0.43

Answer:  P(0.38 < P < 0.43 | n = 1800, P = 0.40) ≈ P(0.38 < P < 0.43 | μ = 0.40, σ = 0.01155)

= P (-1.73 < Z < 2.60)

= 0.4582 + 0.4953 = 0.9535

Difficulty:  Moderate

Topic:  Normal Distribution Approximation for Binomial Distribution

AACSB:  Analytic Skills

Course LO:  Explain the characteristics and applications of continuous probability distributions

 

222) With probability 0.20, the percentage of successes is less than what value?

Answer:  P(P < a | n = 1800, P = 0.40) ≈ P(P < a | μ = 0.40, σ = 0.01155) = 0.20

⇒ P[Z < (a – 0.40) / 0.01155] = 0.20

⇒(a – 0.40) / 0.01155 = -0.84

⇒ a = 0.39 or 39%

Difficulty:  Moderate

Topic:  Normal Distribution Approximation for Binomial Distribution

AACSB:  Analytic Skills

Course LO:  Explain the characteristics and applications of continuous probability distributions

 

223) With probability 0.09 the percentage of successes is greater than what value?

Answer:  P(P > a | n = 1800, P = 0.40) ≈ P(P > a | μ = 0.40, σ = 0.01155) = 0.09

⇒ P[Z > (a – 0.40) / 0.01155] = 0.09

⇒ (a – 0.40) / 0.01155 = 1.34

⇒ a = 0.415 or 41.5%

Difficulty:  Moderate

Topic:  Normal Distribution Approximation for Binomial Distribution

AACSB:  Analytic Skills

Course LO:  Explain the characteristics and applications of continuous probability distributions

 

224) A homeowner has installed a new energy-efficient furnace. It is estimated that over a year the new furnace will reduce energy costs by an amount that can be regarded as a random variable with a mean of $265 and standard deviation of $55. Stating any assumptions you need to make, find the mean and standard deviation of the total energy costs reductions over a period of 5 years.

Answer:  Assume that costs are independent across years.

Let X = Energy costs reductions over a period of one year, and

Y = Energy costs reductions over a period of 5 years.

Then, Y = 5X. Hence, μY = 5μX = (5)(265) = 1325, and σY = 5σX = (5)(55) = 275.

Difficulty:  Moderate

Topic:  Jointly Distributed Continuous Random Variables

AACSB:  Analytic Skills

Course LO:  Explain the characteristics and applications of continuous probability distributions

 

THE NEXT QUESTIONS ARE BASED ON THE FOLLOWING INFORMATION:

Suppose that the time between successive occurrences of an event follows an exponential distribution with mean 1/λ minutes. Assume that an event occurs.

 

225) Show that the probability that more than 4 minutes elapses before the occurrence of the next
event is e-4λ.

Answer:  P(X > 4) = 1 – P(X ≤ 4) = 1 – F(4) = 1 – [1 – e-4λ] = e-4λ

Difficulty:  Moderate

Topic:  The Exponential Distribution

AACSB:  Analytic Skills

Course LO:  Explain the characteristics and applications of continuous probability distributions

 

226) Show that the probability that more than 8 minutes elapses before the occurrence of the next
event is e-8λ.

Answer:  P(X > 8) = 1 – P(X ≤ 8) = 1 – F(8) = 1 – [1 – e-8λ] = e-8λ

Difficulty:  Moderate

Topic:  The Exponential Distribution

AACSB:  Analytic Skills

Course LO:  Explain the characteristics and applications of continuous probability distributions

 

227) Show that, if 4 minutes have already elapsed, the probability that a further 4 minutes will elapse before the next occurrence is e-8λ. Explain your answer in words.

Answer:  P(X > 8 | X > 4) = P(X > 8) / P(X > 4) = e-8λ / e-4λ = e-4λ

The probability of an occurrence within a specified time in the future is not related to how much time has passed since the most recent occurrence.

Difficulty:  Moderate

Topic:  The Exponential Distribution

AACSB:  Analytic Skills

Course LO:  Explain the characteristics and applications of continuous probability distributions

 

THE NEXT QUESTIONS ARE BASED ON THE FOLLOWING INFORMATION:

A continuous random variable X has the probability density function: f(x) = 2e-2x, x ≥ 0.

 

228) What is the distribution of the random variable X?

Answer:  Exponential distribution with λ = 2

Difficulty:  Moderate

Topic:  The Exponential Distribution

AACSB:  Analytic Skills

Course LO:  Explain the characteristics and applications of continuous probability distributions

 

229) Find the mean and standard deviation of X.

Answer:  Mean = Standard deviation = 1/λ = 0.5

Difficulty:  Moderate

Topic:  The Exponential Distribution

AACSB:  Analytic Skills

Course LO:  Explain the characteristics and applications of continuous probability distributions

 

230) What is the probability that x is between 1 and 3?

Answer:  0.1329

Difficulty:  Moderate

Topic:  The Exponential Distribution

AACSB:  Analytic Skills

Course LO:  Explain the characteristics and applications of continuous probability distributions

 

231) What is the probability that x is at most 2?

Answer:  0.9817

Difficulty:  Moderate

Topic:  The Exponential Distribution

AACSB:  Analytic Skills

Course LO:  Explain the characteristics and applications of continuous probability distributions

 

232) When we convert normal distributions to the standard normal distribution, we are essentially making them all alike. How is this possible and what are the implications?

Answer:  Normal distributions are bell-shaped and symmetric around their means. When a normal population is standardized, every value is replaced by a value equal to the number of standard deviations above or below the mean that particular value is. So in a normal population with mean 10 and standard deviation 2, the value 8 becomes z = -1 and so does the value 6 in a normal population with mean 10 and standard deviation 4. So, all normal populations become related to this one standard normal population. That is why, for every normal population 68.26% fall within ±1 standard deviation of the mean, 95.44% fall within 2 and 99.73% fall within ±3. The only thing that really matters for a normal distribution are the standardized z values. Once you know how many standard deviations above or below the mean a value in the normal population is, you can always determine that value and any probabilities about that value.

Difficulty:  Moderate

Topic:  The Normal Distribution

AACSB:  Analytic Skills

Course LO:  Explain the characteristics and applications of continuous probability distributions

 

THE NEXT QUESTIONS ARE BASED ON THE FOLLOWING INFORMATION:

The distribution of IQ scores for high school graduates is normally distributed with mean μ = 104 and standard deviation σ = 16.

 

233) Find the probability a person chosen at random from this group has an IQ score above 146.00.

Answer:  P(X ≥ 146.08) = P(Z ≥ 2.63) = 0.0043

Difficulty:  Moderate

Topic:  The Normal Distribution

AACSB:  Analytic Skills

Course LO:  Explain the characteristics and applications of continuous probability distributions

 

234) What fraction of the IQ scores would be between 97 and 126?

Answer:  P(97 ≤ X ≤ 126) = P(-0.44 ≤ z ≤ 1.38) = 0.5862

Difficulty:  Moderate

Topic:  The Normal Distribution

AACSB:  Analytic Skills

Course LO:  Explain the characteristics and applications of continuous probability distributions

 

235) What is the 95th percentile of this normal distribution?

Answer:  P(X ≥ x0) = 0.05. This implies that P(Z ≥ ) = 0.05

Therefore,  = 1.645. Hence, the 95th percentile is x0 = 130.32.

Difficulty:  Moderate

Topic:  The Normal Distribution

AACSB:  Analytic Skills

Course LO:  Explain the characteristics and applications of continuous probability distributions

 

THE NEXT QUESTIONS ARE BASED ON THE FOLLOWING INFORMATION:

Suppose x is normally distributed with a mean of 75 and a standard deviation of 4.

 

236) Find the 90th percentile.

Answer:  Find x0 such that P(X ≤ x0) = 0.90 = P(Z ≤ z0).

Since the area to the left of z0 is greater than 0.5, z0 must be larger than zero such that P(0 < Z < z0) = 0.40, so z0 = 1.28. Thus, x0 = 75 + (1.28)(4) = 80.12

Difficulty:  Moderate

Topic:  The Normal Distribution

AACSB:  Analytic Skills

Course LO:  Explain the characteristics and applications of continuous probability distributions

 

237) Find the 95th percentile.

Answer:  Find x0 such that P(X ≤ x0) = 0.95 = P(Z ≤ z0).

Since the area to the left of z0 is greater than .5, z0 must be larger than zero such that P(0 < Z < z0) = 0.45, so z0 = 1.645. Thus, x0 = 75 + (1.645)(4) = 81.58

Difficulty:  Moderate

Topic:  The Normal Distribution

AACSB:  Analytic Skills

Course LO:  Explain the characteristics and applications of continuous probability distributions

 

238) Find the 5th percentile.

Answer:  Find x0 such that P(X ≤ x0) = 0.05 = P(Z ≤ z0).

Since the area to the left of z0 is smaller than 0.5, z0 must be smaller than zero such
that P(z0 < Z < 0) = 0.45, so z0 = -1.645. Thus, x0 = 75 + (-1.645)(4) = 68.42

Difficulty:  Moderate

Topic:  The Normal Distribution

AACSB:  Analytic Skills

Course LO:  Explain the characteristics and applications of continuous probability distributions

 

239) A normal random variable x has an unknown mean μ and standard deviation σ = 2.5. If the probability that x exceeds 7.5 is 0.8289, find μ.

Answer:  It is given that x is normally distributed with σ = 2.5 but with unknown mean μ, and
that P (x > 7.5) = 0.8289. In terms of the standard normal random variable z, we can write

P(X > 7.5) = P[Z > (7.5 – μ)/2.5] = 0.8289, Z = -0.95

Since the area to the right of (7.5 – μ)/2.5 is greater than 0.5, then (7.5 – μ)/2.5 must be negative, and that P[(7.5 – μ)/2.5 < z < 0] = 0.3289. Hence, (7.5 – μ)/2.5 = -0.095. This implies μ = 9.875.

Difficulty:  Moderate

Topic:  The Normal Distribution

AACSB:  Analytic Skills

Course LO:  Explain the characteristics and applications of continuous probability distributions