10.9 A problem with a   telephone line that prevents a customer from receiving or making calls is   disconcerting to both the customer and the telephone company. The data in the   file “phone” represent 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 offices are equal, is there evidence of a difference in the mean   waiting time between the two offices? (Use a=0.05) b. Find the p-value in (a)   and interpret its meaning. c. What other assumption is necessary in (a)?    

     Office 1 Office 2   1.48 7.55   1.75 3.75   0.78 0.1   2.85 1.1   0.52 0.6   1.6 0.52   4.15 3.3   3.97 2.1   1.48 0.58   3.1 4.02   1.02 3.75   0.53 0.65   0.93 1.92   1.6 0.6   0.8 1.53   1.05 4.23   6.32 0.08   3.93 1.48   5.45 1.65   0.97 0.72