Should we use t? Determine whether we can safely use a t* critical value to calculate a confidence interval for the population mean in each of the following settings.

(a) We want to estimate the average age at which U.S.

presidents have died. So we obtain a list of all U.S.

presidents who have died and their ages at death.

(b) How much time do students spend on the Internet?

We collect data from the 32 members of our AP®

Statistics class and calculate the mean amount of time that each student spent on the Internet yesterday.

(c) Judy is interested in the reading level of a medical journal.

She records the length of a random sample of 100 words. The Minitab histogram below displays the data.

Frequency 304 25 20- 15 10 S 2 6 8 Word length 10 12