SSC MTS 2022 PYQ — Question 55

The correct answer is option 3 i.e. ₹1,89,000

A sum of 27,000 deposited at compound interest becomes triple of itself after 4 years.

So money after 4 years = 7000 × 3 = 21000

interest + principal = principal (1+ rate/100)^time

⇒ 21000 = 7000  × (1 + rate/100)⁴

⇒ 3 = (1 + (rate/100)⁴

Now cubing both sides,

⇒ 3³ = [1 + (rate/100)⁴]³

⇒ 27 = (1 + rate/100) ^{(4 × 3)}

⇒ 27 = (1 + rate/100)¹²

So from the above equation, we can say that after 12 years money will be 27 times itself.

Hence money after 12 years = 27 × 7000 = 189000