Verizon Wireless would like to estimate the average number of text messages received by American teenagers per month. A random sample of 60 teenaged customers was selected. The sample average was 2,272 messages per month, and the sample standard deviation was 953 messages per month. Construct confidence intervals with the following confidence levels:
a. 90%
b. 95%
c. 99%
d. Verify your results using PHStat.