Under the rule of 72, an investment growing at 8 percent a year doubles in roughly:
A8 years
B72 years
C80 years
D9 years
Answer & Solution
Correct answer: D. 9 years
1. The rule of 72 is a single division.
2. The rule of 72 gives the time required to double a value.
3. It is calculated by taking the number 72 and dividing by the known interest or growth rate.
4. Here that is 72 divided by 8.
5. That gives roughly 9 years.
_Source: OpenStax Principles of Finance (CC BY 4.0), Ch 7 'Time Value of Money I: Single Payment Value'_
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