A camp director is interested in the mean number of letters each child sends during his or her camp session. The population standard deviation is known to be 2.5. A survey of 20 campers is taken. The mean from the sample is 7.9. Find the 99% confidence interval for the mean number of letters.

In the above exercise, compute confidence intervals using Excel and please include the output from Toolpak (or whatever tool you are using), and make sure that you clearly show the following:

1. Confidence level
2. Whether you should use a normal distribution or t-distribution
3. Confidence interval in interval form, i.e., (lower bound, upper bound)
4. Confidence interval in margin of error form, i.e., sample mean margin of error