A problem with a telephone line that prevents a customer from receiving or making calls is upsetting to both the customer and the telephone company. The file Phone contains samples of 20 problems reported to two different offices of a telephone company and the time to clear these problems (in minutes) from the customers' lines:

a. Assuming that the population variances from both offices are equal, is there evidence of a difference in the mean waiting time between the two offices? (Use α = 0.05.)
b. Find the p-value in (a) and interpret its meaning.
c. What other assumption is necessary in (a)?
d. Assuming that the population variances from both offices are equal, construct and interpret a 95% confidence interval estimate of the difference between the population means in the two offices.

Central Office I Time to Clear Problems (minutes) 1.48 1.75 0.78 2.85 0.52 1.60 4.15 3.97 1.48 3.10 1.02 0.53 0.93 1.60 0.80 1.05 6.32 3.93 5.45 0.97 Central Office II Time to Clear Problems (minutes) 7.55 3.75 0.10 10 0.60 0.52 3.30 2.10 0.58 4.02 3.75 0.65 192 0.60 53 4.23 0.08 148 1.65 0.72