A sum of money under compound interest doubles itself in 4 years. In how many years will it become 16 times itself?
Let the initial amount be P.
If it doubles in 4 years, then:
This is a geometric progression where the amount doubles every 4 years. Therefore:
In 4 years → 2P
In 8 years → 4P
In 12 years → 8P
In 16 years → 16P?
It will take 16 years for the amount to become 16 times under compound interest.