A regression analysis with recent UN data from several nations on y = percentage of people who use the Internet, x1 = per capita gross domestic product (in thousands of dollars), and x2 = percentage of people using cell phones has results shown in Table 11.12.

(a) Write the prediction equation.

(b) Find the predicted Internet use for a country with per capita GDP of $10,000 and 50% of the people using cell phones.

(c) Find the prediction equations when cell phone use is

(i) 0%, (ii) 100%, and use them to interpret the effect of GDP.

(d) Use the equations in

(c) to explain the no interaction property of the model.