Posted by jacob on Monday, December 12, 2011 at 10:10pm.
The lifetime of a certain smart phone battery has an
unknown distribution with mean value of 8 hours and
standard deviation of 2 hours. What is the approximate
probability that the average battery lifetime of a sample
of 36 batteries will exceed 8.1 hours?

Statistics  PsyDAG, Wednesday, December 14, 2011 at 11:03am
Assuming a normal distribution,
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.