Question: Suppose that the standard deviation of the tube life for a particular brand of TV picture tube is known to be s = 500, but that the mean operating life is not known. Overall, the operating life of the tubes is assumed to be approximately normally distributed. For a sample of n = 15, the mean operating life is X = 8,900 hr. Determine
(a) the 95 percent and
(b) the 90 percent confidence intervals for estimating the population mean.