If the difference between the compound interest and simple interest on a certain sum at the rate of 5% per annum for 2 years is Rs. 20, then the sum is = ?

Answer: Option D

Let the sum be = 400x
Simple Interest = $$\frac{PTR}{100}$$
S.I = $$\frac{400x\times 2\times 5}{100}$$ = 40x
for Compond Interest 5% = $$\frac{1}{20}$$

C.I = 20x + 20x + x = 41x
Difference = 41x - 40x = 20
i.e. x = 20
∴ Sum is = 400 × 20 = 8000