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 A market research firm supplies manufacturers with estimates of the retail sales of their products from samples of retail stores

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 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 66 units of a small appliance, with a standard deviation of 6.4 units. During the same point in time last year, an SRS of 25 stores had mean sales of 59.024 units, with standard deviation 12.8 units. An increase from 59.024 to 66 is a rise of about 11%.


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




__________ <(μ1−μ2)<_________
( I already tried 0.07767 for the first blank, and 13.1753 for the second blank)


(b) The margin of error is ________
(already tried both the following numbers: 6.01896 and 6.1993)