Compound Interest and the rule of 72

We learned about compound interest today. It is basically the amount of money you make over the years depending on the amount of interest the company makes. Over the years your deposit increases with the interest itself. For example, if you initially deposit $100 and the interest rate of the company is 10% in a year then you money will increase to $110 in the next year. The third year your money will increase with the interest amount earned together. Therefore in the third year you would make 10% of $110, which is $121. The more years you keep your deposit in the company, the more you gain. The ruile of 72 says that in order to find the number of years requires to double your mo ney at a given rate, you can just divide the interst rate into 72. For example, if you want to know how long it will take to double your money at 8% interst, you just simply divide 8 into 72 and you get 9 years. BUT this rule only works if the percentage is less than 20%.