Using the rule of 72 (see the Guide, section G.11.3), how long does it take per capita GDP to double at rates of growth of 0.33 percent per year, 1.5 percent per year, 3 percent per year, 13 percent per year? How long does it take population to quadruple at 0.25 percent per year, 1 percent per year, 2 percent per year? How long does it take population to halve at −0.25 percent per year, −1 percent per year?