In Problem 8.7 we constructed confidence intervals for estimating the mean operating life of a particular brand of TV picture tube based on the assumption that the operating life of all tubes is...

In Problem 8.7 we constructed confidence intervals for estimating the mean operating life of a particular brand of TV picture tube based on the assumption that the operating life of all tubes is approximately normally distributed and s = 500, and given a sample of n = 15 with X = 8,900 hr. Suppose that σ is not known, but rather, that the sample standard deviation is s = 500.

(a) Determine the 95 percent confidence interval for estimating the population mean and compare this interval with the answer to Problem 8.7(a).

(b) Determine the 90 percent confidence interval for estimating the population mean and compare this interval with the answer to Problem 8.7(b).