A shop repairs units in batches, and a study is made to examine the efficiency of the operation of using larger batches. In the data shown below, denotes the number of units in the batch and y, the time, in minutes, required to repair those units. Data for Exercise 3.4 12 3 4 5 56.53 107.83 149.77 185.81 200.19 54.01 112.78 146.06 202.39 226.61 56.80 114.59 159.86 197.48 222.08

a. Fit the linear model y++e, and examine the (xg)-scatter plot and the residual plot to see if the model is acceptable. Show that the quadratic model gives an improved fit but suffers from the lack of variance homogeneity.

b. Show that the model y/z=16+7 assumption of constant variance. + is better with regard to the

c. Develop a prediction interval for I using the model in part (b), and compare with the prediction interval for the linear model from part (a).

d. Comment on the value of associated with the model in part bas compared with either model in part (a). Section 3.3