A P/OM Student Has Purchased a Four-Function Calculator for Use

Multiple Choice

A P/OM student has purchased a four-function calculator for use during exams.This calculator is perfectly reliable except for two parts: its microchip,which has a failure rate of one in every twenty hours of operation; and its battery,which has a failure rate of one in every ten hours of operation.Also,on average the battery will fail in five hours,with a standard deviation of 30 minutes.What service life should the manufacturer specify in order to have a .8413 probability that a battery will not fail within that amount of time?

A) 3.5 hours
B) 4 hours
C) 4.5 hours
D) 5 hours
E) 5.5 hours