How much do you plan to spend for gifts this holiday season? An interviewer asks this question this of 250 customers at a large shopping mall. The sample mean and standard deviation of the response are x=$237 and s=$65.
(a) The distribution of spending is skewed, but we can act as though x is Normal. Why?
(b) For this large sample, we can act as of sigma= $65 because the sample s will be close to the population sigma. Use the sample result to give a 99% confidence interval for the mean gift spending of all adults.
(c) This confidence interval can't be trusted to give information about the spending plans of all adults. Why not?