Rule of 72 - Mathematical wonders
Number of yrs required to double your money at a given rate, U just divide 72 by interest rate
Example :
if you want to know how long it will take to double your
money at 8% interest, divide 72 by 8 and get 9 yrs
At 6% rate, it will take 12 yrs
At 9% rate, it will take 8 yrs