The "Rule of 72" will help you determine all of the following EXCEPT _____?

The "Rule of 72" is a simplified formula that estimates the number of years required to double the investment based on a fixed annual rate of return. This rule is particularly effective for determining how long it will take an investment to grow to twice its original value when interest is compounded at a consistent rate.

When applying the Rule of 72, you can easily calculate how long it will take to double your investment, what annual interest rate is needed to achieve that doubling within a specific timeframe, or even assess the time frame for doubling savings assuming the interest rate remains fixed. Therefore, options related to determining the time it takes to double savings under these fixed conditions are valid applications of the Rule.

However, the distinction arises with variable interest rates. Since the Rule of 72 assumes a constant annual interest rate, it does not effectively apply to situations where rates change frequently. Variable interest rates introduce uncertainty and variability in the growth of an investment, which cannot be captured by the Rule, making it ineffective for assessing the time frame required to double savings in such scenarios.