Question

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 1313 stores this year shows mean sales of 7272 units of a small appliance, with a standard deviation of 66 units. During the same point in time last year, an SRS of 2323 stores had mean sales of 65.4665.46 units, with standard deviation 11.611.6 units. An increase from 65.4665.46 to 7272 is a rise of about 9%.

1. Construct a 95% confidence interval estimate of the difference μ1−μ2μ1−μ2, where μ1μ1 is the mean of this year's sales and μ2μ2 is the mean of last year's sales.

(a)  <(μ1−μ2)<<(μ1−μ2)<

(b) The margin of error is  .

2. At a 0.050.05 significance level, is there sufficient evidence to show that sales this year are different from last year?

A. No
B. Yes

Answer 1