A market research firm supplies manufacturers with estimates of the retail sales of their products from samples of retail stores. Marketing managers are prone to look at the estimate and ignore sampling error. An SRS of 21 stores this year shows mean sales of 68 units of a small appliance, with a standard deviation of 10.8 units. During the same point in time last year, an SRS of 15 stores had mean sales of 57.092 units, with standard deviation 17.1 units. An increase from 57.092 to 68 is a rise of about 16%. 1. Construct a 95% confidence interval estimate of the difference u1 - u2, where u is the mean of this year's sales and u2 is the mean of last year's sales. 1.4626 (#1 - #2)