What is the least number of complete years in which a sum of money, invested at 20% compound interest annually, will more than double?

2 years

3 years

4 years

5 years

Let the principal = ₹100

Rate = 20% per annum, compounded annually

Now calculate the amount over the years:

After 1 year: 100 × 1.20 = ₹120

After 2 years: 120 × 1.20 = ₹144

After 3 years: 144 × 1.20 = ₹172.80

After 4 years: 172.80 × 1.20 = ₹207.36

So, the amount just exceeds double (₹200) after 4 years.