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. Store's Card Major Credit Card
Sample size 64 49
Sample mean $140 $125
Population standard deviation $10 $8

Required:
a. A 95% confidence interval estimate for the difference between the average purchases of all customers using the two different credit cards is:
b. 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 to ? The test statistic for an α of 0.05 is :