# MATH

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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 -

Z = (x - mean)/SD = (322-300)/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.

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