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 12 stores this year shows mean sales of 55 units of a small appliance, with a standard deviation of 12.8 units. During the same point in time last year, an SRS of 23 stores had mean sales of 43.608 units, with standard deviation 14.8 units. An increase from 43.608 to 55 is a rise of about 21%.

1: Construct a 99% confidence interval estimate of the difference 12, where 1 is the mean of this year's sales and 2 is the mean of last year's sales.

_______<(12)<______

2. What is the margin of error?

3. At a 0.01 significance level, is there sufficient evidence to show that sales this year are different from last year? (Y or N)