The management of a department store is interested in estimating the difference between the mean credit purchases of customers using the store's credit card versus those customers using a national major credit card. You are given the following information. Sample size Sample mean Population standard deviation a b. a. b. C. Store's Card 64 $140 $10 Major Credit Card 49 15 3.32 11.68 to 18.32 $125 $8 A point estimate for the difference between the mean purchases of the users of the two credit cards is At 95% confidence, the margin of error is C. A 95% confidence interval estimate for the difference between the average purchases of the customers using the two different credit cards is ANS: