Rule of 72

I learned an interesting & easy rule, the Rule of 72, to get the estimation of how long an investment will double with a given rate of return, or with a target timeline, find out how much rate of return need to obtain.

A simple example:
Cymbeline bought a house for RM200K, and in 8 years time, the house's value increase to RM400K, what is the inflation rate?
Simple Answer: 72/8years= 9%

Christabel has RM60K, she wants to know when she can double her investment with the interest of 10%.
Simple Answer: 72/10= 7.2years

Interesting right? haha ^^v