A sum of ₹ 600 put at 5% S.I. amounts to ₹ 720 in:

1. 3 years

2. 4 years

3. 5 years

4. 6 years

Given:

P = ₹ 600

R = 5%

A = ₹ 720

Let the time be $t$.

$\text{A = P + S.I.}\\[1em] \Rightarrow ₹ 720 = ₹ 600 + \text{S.I.}\\[1em] \Rightarrow \text{S.I.} = ₹ 720 - ₹ 600\\[1em] \Rightarrow \text{S.I.} = ₹ 120\\[1em]$

And

$\text{S.I.} = \Big(\dfrac{P \times R \times T}{100}\Big)\\[1em] \Rightarrow 120 = \Big(\dfrac{600 \times 5 \times t}{100}\Big)\\[1em] \Rightarrow 120 = \dfrac{3,000 \times t}{100}\\[1em] \Rightarrow 120 = 30 \times t\\[1em] \Rightarrow t = \dfrac{120}{30}\\[1em] \Rightarrow t = 4$

Hence, option 2 is the correct option.