A manufacturer knows that their items have a normally distributed length, with a mean of 12.9 inches, and standard deviation of 2.6 inches.
If 20 items are chosen at random, what is the probability that their mean length is less than 14.2 inches?
Z = (score-mean)/SD/√n
Find table in the back of your statistics text labeled something like "areas under normal distribution" to find the proportion/probability for the Z score.