In this case 100 would be the interest but it would still be 10. Watch Khan Academys video on compound interest BEFORE moving on to the evaluation section. The formula for compound interest is P 1 rn nt where P is the initial principal balance r is the interest rate n is the number of times interest is compounded per time period and t is the number of time periods.
So if you just take 72 and divide it by 1 you get 72.
T Time Period involved in months or years. In this case 100 would be the interest but it would still be 10. From the base formula A P 1 rt derived from A P I and I Prt so A P I P Prt P 1 rt Note that rate r and time t should be in the same time units such as months or years. This math video tutorial explains how to use the simple interest formula to solve word problems.