Posted by Michelle on .
Electricalc has determined that the assembly time for a particular electrical component is normally distributed with a mean of 20 minutes and a variance of 9 minutes.
a. What is the probability that an employee in the assembly division takes longer than 22 minutes to assemble one of these component?
b. What is the probability that the average assembly time for 15 such employees exceeds 22 minutes?

STAT 
PsyDAG,
a. Use same process as previous post.
b. Because you are dealing with means (average) rather than individual scores:
Z = (scoremean)/SEm
SEm = SD/√n
Find table in the back of your statistics text labeled something like "areas under normal distribution" to find the proportion related to the Z score.