Citibank, which has a major credit card division, has designed a promotion that the firm hopes will encourage its customers to increase their current credit card usage. To test the effectiveness of the promotion, Citibank monitored the monthly balances of 25 customers who were informed of the promotion and the monthly balances of 25 customers who were not aware of it. Assume the population variance for the credit card balances are equal. The results can be found in the Excel file Citibank 2. xlsx.

a. Using α = 0.05, perform a hypothesis test to determine if the average credit card balance is higher for customers aware of the promotion than it was for customers unaware of the promotion.

b. Construct a 90% confidence interval to estimate the average difference in credit card balance before and after the promotion.

c. Verify your results using PHStat.

d. Identify the p value and interpret the result.

e. What assumptions need to be made in order to perform this procedure?