A study of the amount of time it takes a mechanic to rebuild the transmission for a 1992 Cavalier shows that the mean is 4.5 hours and the standard deviation is .6 hours. If 42 mechanics are randomly selected, find the probability that their mean rebuild time is less than 3.5 hours.

Answer 1

Z = (score-mean)/SEm

SEm = SD/√n

Find table in the back of your statistics text labeled something like "areas under normal distribution" to find the proportion/probability related to the Z score.

Answer 2

I'm not quite sure I understand. What do I use as the score, and what do I use for n.