How long would it take to double a $100,000 investment at a 9% annual return according to the Rule of 72?

To determine how long it would take to double an investment using the Rule of 72, one needs to divide 72 by the annual interest rate. In this case, with an investment returning 9% per year, the process involves calculating:

72 / 9 = 8

This means that it would take approximately 8 years to double a $100,000 investment at a 9% annual return. The Rule of 72 is a simplified formula used in finance to estimate the number of years required to double the investment based on a fixed annual rate of return. By applying this rule effectively, one can quickly gauge investment growth potential over time without resorting to more complex mathematical calculations.

The other options reflect either too short or too long a period for doubling the investment at that rate, thereby emphasizing the effectiveness and practical use of the Rule of 72 in estimating investment growth.