Refer to Exercise 10.

What sample size is necessary so that a 95% confidence interval will have a margin of error of 1 hour?

Exercise 10

The amount of time that a certain cell phone will keep a charge is known to be normally distributed with standard deviation

σ = 16 hours. A sample of 40 cell phones had a mean time of 141 hours. Let μ represent the population mean time that a cell phone will keep a charge.