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The mean life of 20 printers is 1014 hours. Their lifetimes are normally distributed with σ...

The mean life of 20 printers is 1014 hours. Their lifetimes are normally distributed with σ = 25 hours. Which of the following is the smallest number of sample size that assures if we wanted to be 95% confident that the error in estimating the mean life is less than 5 hours?

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Answer #1

We want to be 95% confident that the error in estimating the mean life is less than 5 hours.

This is means that are margin of error needs to be less than 5 hours

This if for population mean and we hvae the population SD therefore we will use the normal distribution to calculate the C.V

Margin of error = C.v. * SE

Margin of error =

= 1 - 0.95 = 0.05

C.V. = Z0.025

  = 1.96 using normal distribution tables

σ = 25

SE = 25 /

MOE = 1.96 * 25 /

MOE < 5

1.96 * 25 / <5

n > 96.04

n= 96

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