Posted by mike on .
The mean life of a set of batteries in a T83 calculator is 525 with a standard deviation of 35 hours assume normal distribution is normal whats is the probability that set will last for more the 540 hrs

statistics 
PsyDAG,
Z = (scoremean)/SD
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.