A telephone company wants to estimate the mean length of long-distance calls during weekends.

A. random sample of 50 such calls gives a mean of 14.5 minutes and a standard deviation of 5.6 minutes. a. What / who is the population?

b. What / who is the sample?

c. What quantity are we interested in estimating? Hint: The answer to this question is NOT a number. (It is a sentence describing what the number we are trying to estimate represents.)

d. Check that the conditions to build a confidence interval are satisfied. State whether the critical value is from a Z-distribution or a T-distribution and why.

e. Find the margin of error for a 98% confidence interval. Round to the nearest tenth.

f. Find a 98% confidence interval. Round to the nearest tenth.

g. Interpret the confidence interval.