During manufacture, the thickness of laser printer paper is monitored. Data from several random samples each day during the year suggest that thickness follows a normal distribution. A sample of M = 10 thickness measurements (ten-thousandths inch) yields the 95% confidence interval (4.33, 11.50) for σ2.
(a) What was the standard deviation s for the sample? (Examine how s enters the formula of a confidence interval.)
(b) Calculate a 90% confidence interval for a.