Automobile dealers usually advertise in the yellow pages of the telephone book. Sometimes they have to pay to be listed in the white pages, and some dealerships opt to save money by omitting that listing, assuming most people will use the yellow pages to find the telephone number. A two-year study is conducted with 20 car dealerships where in one year the dealer is listed in the white pages and the other year it is not. Ten of the dealerships are listed in the white pages the first year and the other 10 are listed there in the second year in an attempt to control for economic cycles. The following data represent the numbers of units sold per year. Is there a significant difference between the number of units sold when the dealership is listed in the white pages and the number sold when it is not listed?
Assume all companies are continuously listed in the yellow pages, that the t test is not appropriate, and that α =.01.

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