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 23
stores this year shows mean sales of 56
units of a small appliance, with a standard deviation of 13.4
units. During the same point in time last year, an SRS of 11
stores had mean sales of 43.538
units, with standard deviation 11.1
units. An increase from 43.538
to 56
is a rise of about 22%.
1. Construct a 95% confidence interval estimate of the difference μ1−μ2
, where μ1
is the mean of this year's sales and μ2
is the mean of last year's sales.
(a)
equation editorEquation Editor <(μ1−μ2)<
equation editorEquation Editor
(b) The margin of error is
equation editorEquation Editor .
2. At a 0.05
significance level, is there sufficient evidence to show that sales this year are different from last year?
A. No
B. Yes
