At 20% per annum rate, an amount is doubled in approximately in _________ years at compound interest.

Correct option is C

Given:

Compound Interest Rate = 20% per annum

Final Amount = 2 × Principal (the amount is doubled)

Formula Used:

​$$A = P(1 + \frac{r}{100})^t$$​​

Solution: 

Amount is double, so;

2P = $$P(1 + \frac{20}{100})^t$$​​

2 = $$(1.2)^t$$​​

Now , by options:

Option A: (1.2)⁵ = 2.48832 → Too high

Option B: (1.2)² = 1.44 → Too low

Option C: (1.2)⁴ = 2.0736 → Closest to 2

Option D: (1.2)³ = 1.728 → Less than 2