A sum of Rs. 12000 deposited at compound interest becomes

A sum of Rs. 12000 deposited at compound interest becomes doubles after 5 years. After 20 years it will become ?

∵ 2P = P(1 +r/100)⁵
⇒ (1 +r/100)⁵ = 2
∴ (1 + r/100)²⁰ = 2⁴ = 16
Thus, P(1 +r/100)²⁰ = 16P
= Rs. (12000 x 16)
= Rs. 192000