Suppose that the standard deviation of the tube life for a particular brand of TV picture tube is known to be 500, but that the mean operating life is not known. Overall, the operating life of the...

Suppose that the standard deviation of the tube life for a particular brand of TV picture tube is

known to be 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 8,900 hr. Determine (a) the 95 percent and (b) the 90 percent confidence intervals

for estimating the population mean.