year. The mean increase is $342, and the standard deviation is $108. (a) Is there signicant evidence at the 1% level that the mean amount charged increases under the no-fee offer? State Hand H3 and carry out a ttest. (b) Give a 95% condence interval for the mean amount of the increase. (c) The distribution of the amount charged is skewed to the right, but outliers are prevented by the credit limit that the bank enforces on each card. Use of the t procedures is justied in this case even though the population distribution is not normal. Explain why