If the economy's real GDP doubles in 9 years, we can conclude that its average annual rate of growth is 8%.
The rule of 72 can be used to determine when the real GDP of an economy would double. In order to determine the doubling time, divide 72 by average annual rate of growth.
average annual rate of growth = 72 / average annual rate of growth
72 / 9 = 8%
To learn more about real GDP, please check: https://brainly.com/question/15225458