Mostly when we invest or save money, we want to know when it will be doubled. Here I give you the simple tip, j, you just divide 72 by the interest rate number like if you are getting 7% interest on your saving or investment just divide 72 by 7, you will get 10.3 it means you money is going to be double in approx 10 years 3 months.
Doubling money period can help to achieve your financial goal and investment required to achieve that goal. Similarly, if you want to know when your money will become 4 time of your investment then divide 144 by the offered rate mean in our case 7% then it should be 144 divide by 7(144/7) and answer is 20 years 6 month appox.