A sum of ₹7,000 deposited at compound interest becomes triple of itself after 4 years. How much will the amount be after 12 years?

₹1,89,000

Three times of sum = 3 × 7000 = 21000

Amount = P$(1 \;+\; \frac{R}{100})^t$

21000 = 7000 [ 1 + \(\frac{R}{100}\) ]4

3 = [ 1 + \(\frac{R}{100}\) ]⁴ 

To find sum after 12 years.

On cubing both side,

3³ = [ 1 + \(\frac{R}{100}\) ]¹²

27 = [ 1 + \(\frac{R}{100}\) ]¹²

So, Sum becomes 27 times of itself after 12 years .

i.e. 27 × 7000 = Rs. 189000