If the difference between simple interest and compound interest for 4 years is Rs.32.60 at 10% per annum compounded biannually on a certain sum of money. Find the sum of money.

For compound interest compounded biannually at 10% per annum, the rate per half-year period is 5% and there are 8 half-year periods in 4 years. The difference between compound interest and simple interest for 4 years is given as Rs.32.60. Using the formula for this difference and solving for the principal P, we get P = 32.60 × 10000 / 400 = Rs.815. Option C is correct.