Arun invests an amount of ₹4,000 at the rate of 2% simple interest per annum. For how many years did he invest the amount to double his sum?

50 years

Principal Invested =4000

Rate of interest = 2% p.a.

If Amount A, required is double = 2*P = 8000 

Simple Interest = A-P = 4000 = P*R*T/100 = 4000*2*T/100

2T = 100

T = 50

The correct answer is Option (3) → 50 years