Final answer:
The Rule of 72 is a quick formula to determine the time required for an investment to double in value at a steady growth rate. By dividing 72 by the annual growth rate, you get the doubling time in years.
Step-by-step explanation:
The Rule of 72 is a simple formula used to estimate the number of years it will take for an investment or economy to double in size, given a fixed annual growth rate. You just divide the number 72 by the annual percentage growth rate. For example, if the annual growth rate is 6%, you would calculate 72 divided by 6, which equals 12 years for the investment or economy to double. To use the Rule of 72 to estimate how long it will take for India, Spain, and South Africa to double their standards of living, you would need the annual growth rate of their economies. Once you have that, you can apply the Rule of 72 to find out the doubling time for each country.