The manager of a major retail clothing store claims that the mean monthly purchases by customers who use the store's in-house credit card is larger than the mean monthly purchases by customers who use a Visa, Mastercard, or one of the other major credit cards. To test her claim, she selects a random sample of customers who have made one or more purchases with each of the types of credit cards. The following represents the results of the sampling:

In-House Credit Card Major Credit Cards

Sample Size: 98 134

Sample Mean: $52.33 $49.87

Sample Standard Deviation: $12.90 $14.47

Assuming equal population variances, use Excel to answer the following questions:

a. Using hypothesis testing with the significance level of 0.05, determine whether the mean monthly purchases by customers using in-house credit card exceeds that of major credit cards. Formulate your null and alternative hypotheses and justify your decision using the p-value. What is the p-value and what does it measure in this context?

b. Using the sample data and excel, construct an 90% confidence interval estimate for the difference in mean monthly purchases by customers using the two types of credit cards. On the basis of the confidence interval produced, does it appear that there is a statistically significant difference between the mean monthly purchases by customers using the two types of credit cards? Explain your answer.

c. Are your answers to Parts a and b above the same? Why/Why not? Explain your observation and justification.