9.11. Figure 9.21 is a scatterplot relating y = percent of people using cell phones and x = per capita gross domestic product (GDP) for nations listed in the Human Development Report.

(a) Give the approximate x- and _v-coordinatcsfor the nation that has the highest (i) cell-phone use, (ii) GDP.

(b) The least squares prediction equation is y =

-0.13 + 2.62a:. For the U.S., x = 34.3 and y = 45.1. Find the predicted cell-phone use and the residual. Interpret the residual.

(c) Is the correlation positive, or negative?

Explain what it means for the correlation to have this sign.