Use the Rule of 72 to estimate how long it will take for India, Spain, and South Africa to double their standards of living.

Rule of 72

It is worth pausing a moment to marvel at the East Asian Tigers' growth rates. If per capita GDP grows at, say, 6% per year, then you can apply the formula for compound growth rates-that is (1 + 0.06)³⁰-meaning a nation's level of per capita GDP will rise by a multiple of almost six over 30 years. Another strategy is to apply the rule of 72. The rule of 72 is an approximation to figure out doubling time. We divide the rule number, 72, by the annual growth rate to obtain the approximate number of years it will take for income to double. If we have a 6% growth rate, it will take 72/6, or 12 years, for incomes to double. Using this rule here suggests that a Tiger that grows at 6% will double its GDP every 12 years. In contrast, a technological leader, chugging
along with per capita growth rates of about 2% per year, would double its income in 36 years.