7.30 Credit card fees.
A bank wonders whether omitting the annual credit card fee for customers who charge at least $5000 in a year would increase the amount charged on its credit card. The bank makes this offer to an SRS of 125 of its existing credit card customers. It then compares how much these customers charge this year with the amount that they charged last year. The mean is $685, and the standard deviation is $1128.