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Chapter 7
Continuous Probability Distributions
Multiple Choice
38. The mean of any uniform probability distribution is
A) (b  a)/2
B) (a + b)/2
C)
Σ
x/η
D) n
π
Answer: B
44. Which of the following is NOT true regarding the normal distribution?
A) Mean, median and mode are all equal
B) It has a single peak
C) It is symmetrical
D) The points of the curve meet the Xaxis at z = –3 and z = 3
Answer: D
46. For a standard normal distribution, what is the probability that z is greater than 1.75?
A) 0.0401
B) 0.0459
C) 0.4599
D) 0.9599
Answer: A
47. What is the area under the normal curve between z = 0.0 and z = 1.79?
A) 0.4633
B) 0.0367
C) 0.9599
D) 0.0401
Answer: A
48. What is the area under the normal curve between z = –1.0 and z = –2.0?
A) 0.0228
B) 0.3413
C) 0.1359
D) 0.4772
Answer: C
49. What is the area under the normal curve between z = 0.0 and z = 2.0?
A) 1.0000
B) 0.7408
C) 0.1359
D) 0.4772
Answer: D
50. The mean amount spent by a family of four on food per month is $500 with a standard deviation of
$75. Assuming that the food costs are normally distributed, what is the probability that a family spends
less than $410 per month?
A) 0.2158
B) 0.8750
C) 0.0362
D) 0.1151
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52. What is the proportion of the total area under the normal curve within plus and minus two standard
deviations of the mean?
A) 68%
B) 99.7%
C) 34%
D) 95%
Answer: D
53. The mean score of a college entrance test is 500; the standard deviation is 75. The scores are
normally distributed. What percent of the students scored below 320?
A) About 50.82%
B) About 34.13%
C) About 7.86%
D) About 0.82%
Answer: D
54. The mean of a normally distributed group of weekly incomes of a large group of executives is $1,000
and the standard deviation is $100. What is the zscore for an income of $1,100?
A) 1.00
B) 2.00
C) 1.683
D) 0.90
Answer: A
55. A new extendedlife light bulb has an average service life of 750 hours, with a standard deviation of
50 hours. If the service life of these light bulbs approximates a normal distribution, about what percent of
the distribution will be between 600 hours and 900 hours?
A) 95%
B) 68%
C) 34%
D) 99.7%
Answer: D
56. A study of a company's practice regarding the payment of invoices revealed that an invoice was paid
an average of 20 days after it was received. The standard deviation equaled five days. Assuming that the
distribution is normal, what percent of the invoices were paid within 15 days of receipt?
A) 15.87%
B) 37.91%
C) 34.13%
D) 86.74%
Answer: A
57. An accelerated life test on a large number of typeD alkaline batteries revealed that the mean life for
a particular use before they failed is 19.0 hours. The distribution of the lives approximated a normal
distribution. The standard deviation of the distribution was 1.2 hours. About 95.44 percent of the
batteries failed between what two values?
A) 8.9 and 18.9
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 Spring '10
 BARCUS

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