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Question 6

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True or False: The proportion of the population that has certain characteristics is the same as the probability that a randomly selected individual of the population has these same characteristics.

Select one:

A. True

B. False

Question 7

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The tread life of a particular brand of tire is a random variable best described by a normal distribution with a mean of 60,000 miles and a standard deviation of 3000 miles. What warranty should the company use if they want 96% of the tires to outlast the warranty?

Select one:

A. 54,750 mi

B. 63,000 mi

C. 65,250 mi

D. 57,000 mi

Question 8

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The length of time it takes college students to find a parking spot in the library parking lot follows a normal distribution with a mean of 5.5 minutes and a standard deviation of 1 minute. Find the cut-off time which 75.8% of the college students exceed when trying to find a parking spot in the library parking lot.

Select one:

A. 6.0 min

B. 6.2 min

C. 5.8 min

D. 6.3 min

Question 9

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A new phone system was installed last year to help reduce the expense of personal calls that were being made by employees. Before the new system was installed, the amount being spent on personal calls follows a normal distribution with an average of $800 per month and a standard deviation of $50 per month. Refer to such expenses as PCE's (personal call expenses). Find the point in the distribution below which 2.5% of the PCE's fell.

Select one:

A. $898.00

B. $20.00

C. $702.00

D. $780.00

Explanation / Answer

a)The proportion of the population that has certain characteristics is the same as the probability that a randomly selected individual of the population has these same characteristics is always true

so answer is true

b)

mean = 60000

standard deviation = 3000

let the warranty distance be D

P(X>D) = 0.96

P(X<=D) = 0.04

z value for 96% or 0.04 using z table is -1.75

so (D-60000)/3000 = -1.75 => D = 60000-3000*1.75 = 54750 (A)

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