A first-aid cream contains amounts of the active ingredient (in mg) that vary Normally with unknown mean m and standard deviation s from tube to tube. You select a simple random sample of 9 tubes and assess the quantity of active ingredient they contain. The 9 amounts, in mg, are 23 24 23 29 28 26 27 28 26 Based on these data, a 99% confidence interval for the population mean m has margin of error of mg.