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 1.77 hours.
Assume that a random sample of 40 mechanics is selected and the mean rebuild time of the sample is computed. Assuming the mean times are normally distributed, what percentage of sample means are greater than 9.1 hours?

Question

Quizplus · Accepted Answer

The standard error of the mean is calculated as the standard deviation divided by the square root of the sample size. Using this, we find the z-score for 9.1 hours and then use the standard normal distribution to find the percentage of sample means greater than 9.1 hours.

A Study of the Amount of Time It Takes a Mechanic