Posted by Ty on .
Battery Power Problem. A certain type of thermal battery
for an airplane navigation device backup power has a
mean life of 300 hours with a standard deviation of 15
hours. What proportion of these batteries can be
expected to have lives of 322 hours or less? Assume a normal
distribution of backup power device lives.

MATH 
PsyDAG,
Z = (x  mean)/SD = (322300)/15
Find table in the back of your statistics text labeled something like "areas under normal distribution" to find the proportion below the Z score found from above.