Maths Trick Time taken to double the money

You might have heard about time taken to double your invested money in X no. of years when agents are marketing about their product instead of straight away telling about effective rate of interest.

So i am sharing you a trick to calculate rate of interest to double the amount if you know the time or
vice versa in a matter of 3 seconds.

Scope of formula :
applicable to compound interest
gives you a rough idea may or may not be accurate
Applicable to double the amount

Formula
(Time taken to double Invested money) X (Rate of interest) = 72

Formula Check
rate of interest be 10 % annualy, Investment amount Rs. 100000
using formula
Time
= 72 / Rate of interest
= 72/10
= 7.2 years

Amount = p  [(1+R%)^t]
=100000 [(1+10/100)^7.2]
=100000[(1.1)^7.2]
=198621.99

Formula Pass
:)

If like the trick say Thanks