# Point Estimate and Confidence Interval

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

a)A point estimate for the difference between the mean purchases of the users of the two 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

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#### Solution Preview

Please see attached file:

Confidence interval for difference between means (large sample size)

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

Data

Sample 1: Store's Card

Mean of sample 1= M1 = $140

Standard deviation of sample 1= s1 = $10 ...

#### Solution Summary

Calculates the point estimate and confidence interval for the difference between the mean purchases of the users of the two credit cards.