Using this copier maintainance data below, The users of the copiers are either training institutions that use a small model, or business firms that use a large, commercial modeL. An analyst at Tri-City wishes to fit a regression model including both number of copiers serviced (XI) and type of copier (X2 ) as predictor variables and estimate the effect of copier model (S-small, L-large) on number of minutes spent on the service call. Records show that the models serviced in the 45 calls were:

Assume that regression model is appropriate, and let X2 = I if small model and 0 if large, commercial model. a. Explain the meaning of all regression coefficients in the model. b. Fit the regression model and state the estimated regression function. c. Estimate the effect of copier model on mean service time with a 95 percent confidence interval. Interpret the interval estimate. d. Why would the analyst Wish to include X I, number of copiers, in the regression model when interest is in estimating the effect of type of copier model on service time? e. Obtain the residuals and plot them against X1X2 Is there any indication that an interaction term in the regression model would be helpful?

Y(service time)	X1(number of copiers serviced)
20	2
60	4
46	3
41	2
12	1
137	10
68	5
89	5
4	1
32	2
144	9
156	10
93	6
36	3
72	4
100	8
105	7
131	8
127	10
57	4
66	5
101	7
109	7
74	5
134	9
112	7
18	2
73	5
111	7
96	6
123	8
90	5
20	2
28	2
3	1
57	4
86	5
132	9
112	7
27	1
131	9
34	2
27	2
61	4
77	5