Refer to the previous exercise.

(a) Show how to obtain R-squared from the sums of squares in the ANOVA table. Interpret it.

(b) r2 = 0.78 when GDP is the sole predictor. Why do you think R2 does not increase much when cell phone use is added to the model, even though it is itself highly associated with y (with r = 0.67)? (Hint:Would you expect x1 and x2 to be highly correlated? If so, what is the effect?)