The 'rule of 72' is a simplified way to determine how long an investment will take to double,
given a fixed annual rate of interest. By dividing 72 by the annual rate of return, investors
can get a rough estimate of how many years it will take for the initial investment to duplicate
itself. For example, the rule of 72 states that $1 invested at 10% would take 7.2 years
((72/10) = 7.2) to turn into $2. In reality, a 10% investment will take 7.3 years to
double ((1.10 * 7.3 = 2).