A bank wonders whether omitting the annual credit card fee for customers who charge at least $2500 in a year will increase the amount charged on its credit cards. The bank makes this offer to an SRS of 200 of its credit card customers. It then compares how much these customers charge this year with the amount that they charged last year. The mean increase in the sample is $346, and the standard deviation is $112. The distribution of the amount charged is skewed to the right, but outliners are prevented by the credit limit that the bank enforces on each card.
Can we use a confidence interval based on a Normal sampling distribution for the sample mean x-bar?
A confidence interval can be used because the sample is large and there are no outliners.
A confidence interval cannot be used because the distribution of the amount charged is skewed.
A confidence interval cannot be used because the sample is small.