A certain brand of hand-held computer runs on four 1.5-volt AAA batteries. The mean battery life of a sample of 25 such computers is found to be 60.1 hours and the standard deviation is 4.3 hours.
(a) Find and interpret a 99% confidence interval for the mean battery life of this make of computer.
(b) Determine the sample size required to have a margin of error of 0.5 hours and a 99% confidence level.