Question

According to the rule of 72, if Arielle invests $100, $200, and $2000 into three separate accounts with the same interest rate, which amount will double fastest?

Answer 1

All of them will double at the same time.

Explanation:

The rule of 72 wa created to have an estimate of how long will an account that pays interests will take to double its value, in this case, as they all have the same interest rate, and the rule of 72 depends only on the interests that the account pays, there will be no difference between the doubling time of the accounts since eventhough they all have different amounts of money, having the same interest rate, will make them grow at the same rate.

Answer 2

The rule of 72 is an approximate estimate of the time it takes to double an investment, and depends only on the interest rate. So amount of deposit does not change the estimate. All three accounts will take the same time to double.

If the accounts are all deposited on the same day with the same interest rate and same compounding period, they all double at the same time, whether using the rule of 72 or the actual time.