Question: A manufacturer of cookies and crackers does a survey of the age at sale of one of its brands. A random sample of 23 retail markets in a particular region is chosen. In each store, the number of days since manufacture of the frontmost box of crackers is determined by a date code on the box. The data (age in days) are:

27 34 36 36 38 39 39 39 40 40 42 45 47 51 52 57 63 71 75 84 96 110 147

Knowing that sigma for the population of cookies and crackers is known, compute the 99% confidence interval for the true mean age