Two years ago, a car dealership reported that on average, a customer who chooses

Question

Two years ago, a car dealership reported that on average, a customer who chooses to get his/her car serviced at the shop would wait about 130 minutes with the standard deviaiton of 26 minutes. A student who wanted to evaluate the accuracy of the claim took a sample of 40 customers who got their auto repaird done at the shop.

1. What is the probability that this student will find an average service time exceeding 136 minutes?

2. Based on his sample, what is the probability that ths student will fine the mean repair time to be between 124 minutes and 136 minutes?

Explanation / Answer

a) Mean = 130

SD = 26

n = 40

z = (136 - 130)/26/40

z = 1.46

P = 0.07215

b) z1 = (124 - 130)/26/40

z1 = - 1.46

P( -1.46 <z < 1.46) = 0.8557

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