Is there a difference in the prices at a warehouse club such as Costco and store brands?

Question:

Is there a difference in the prices at a warehouse club such as Costco and store brands? To investigate this, a random sample of 10 purchases was selected, and the prices were compared. (Data extracted from "Shop Smart and Save Big," Consumer Reports, May 2009, p. 17.) The prices for the products are stored in Shopping 1.
a. At the 0.05 level of significance, is there evidence of a difference between the mean price of Costco purchases and store-brand purchases?
b. What assumption is necessary about the population in order to perform this test?
c. Construct a 95% confidence interval estimate of the mean difference in price between Costco and store brands. Interpret the interval.
d. Compare the results of (a) and (c). Distribution
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