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
Sample size 64
Sample mean $140
Population standard deviation $10
Major Credit Card
Sample size 49
Sample mean $125
Population standard deviation $8
a. At 95% confidence, the margin of error is how much?
b. A 95% confidence interval estimate for the difference between the average purchases of all customers using the two different credit cards is?
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