The ability of a grocery store scanner to read accurately is measured in terms of maximum attenuation (db). In one test with 20 different products, the values of this measurement had a mean 10.7 and standard deviation 2.4. The normal assumption is reasonable.
(a) Is there strong evidence that p, the population mean maximum attenuation for all possible products, is greater than 9.25 db?
(b) Give a 98% confidence interval for the mean maximum attenuation.