Question

helpppp...Thurman put $90 into an account that pays 4.4% interest, compounded quarterly. According to the rule of 72, approximately how long will it take for his money to double?

Answer 1

The rule says that the time for the principal to double is found by dividing 72 by the interest percentage per period. In this case the number of periods will be 72/1.1. The the result in years is found by dividing that result by four:
\[time=\frac{72}{1.1}\times \frac{1}{4}=?\ years\]