Question

A study of the amount of time it takes a mechanic to rebuild the transmission for a 1992 Chevrolet Cavalier shows that the mean is 8.4 hours and the standard deviation is 1.8 hours. If 40 mechanics are randomly selected, find the probability that their mean rebuild time exceeds 9.1 hours.

Answer 1

The probability is 0.0069

Explanation:

First thing to do here is to calculate the z-score

Mathematically;

z-score = (x-mean)/SD/√(n)

where x = 9.1 , mean = 8.4 , SD = 1.8 and n = 40

Plugging these values into the z-score equation, we have;

z-score = (9.1-8.4)/1.8/√(40) = 0.7/1.8/6.325 = 0.0615

Now, we check the standard normal table for P(z > 2.46) = 0.0069