30. An important issue for a retailer is to decide when to reorder stock from a supplier.

A common policy used to make the decision is of a type called s, S: The retailer orders at the end of a period if the on-hand stock is less than s, and orders enough to bring the stock up to S. The appropriate values of s and S depend on different cost parameters, such as inventory holding costs and the profit per item sold, as well as the distribution of the demand during a period. Consequently, it is important for the retailer to collect data relating to the parameters of the demand distribution.

Suppose that the following data give the numbers of a certain type of item sold in each of 30 weeks.

14, 8, 12, 9, 5, 22, 15, 12, 16, 7, 10, 9, 15, 15, 12, 9, 11, 16, 8, 7, 15, 13, 9, 5, 18, 14, 10, 13, 7, 11 Assuming that the numbers sold each week are independent random variables from a common distribution, use the data to obtain a 95 percent confidence interval for the mean number sold in a week.