The difference between the compound interest and simple interest on Rs x at 9% per annum for 2 years is Rs 20.25. What is the value of x?

For 2 years, the difference between compound interest and simple interest on the same principal is P(r/100)^2, where P is the principal amount and r is the rate. Here, Difference = x × (9/100)^2 = x × 0.0081 = 20.25. Solving for x: x = 20.25 ÷ 0.0081 = 2500. This formula holds because compound interest includes interest on interest, while simple interest is calculated only on the original principal.