10.9

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:

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 1.10 0.60 0.52 3.30 2.10 0.58 4.02

3.75 0.65 1.92 0.60 1.53 4.23 0.08 1.48 1.65 0.72

a. Assuming that the population variances from both of-

fices are equal, is there evidence of a difference in the

mean waiting time between the two offices? (Use = 0.05.)

b. Find the p-value in (a) and interpret its meaning.

c. What other assumption is necessary in (a)?