13.15 Price of used cars For the 19 used cars listed in the Used Cars data file on the book’s website (see also Exercise 13.11), modeling the mean of y = used car price in terms of x1 = age results in r2 = 0.66.

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Adding x2 = horsepower (HP) to the model yields the results in the following display. Regression Equation Price 19349-1406 Age + 25.5 HP Coefficients Term Coef SE Coef T-Value P-Value Constant 19349 4053 4.77 0.000 Age -1406 320 -4.40 0.000 HP 25.5 22.3 1.14 0.270 Model Summary S 2084.69 R-sq 68.69% Analysis of Variance Source DF SS MS F-value P-value Regression 2 152567500 76283750 17.55 0.000 Error Total 16 69534753 4345922 18 222102253 a. Report R and show how it is determined by SS values in the ANOVA table. b. Interpret its value as a proportional reduction in pre- diction error. c. Interpret its value as the percentage of the variability in the response variable that can be explained.