A certain principal amount yields Rs. 660 as simple interest over 2 years, while the compound interest for the same period is Rs. 696.30. If the interest rate remains constant in both cases, what is the rate of interest?

Explanation

The difference between compound interest and simple interest for 2 years is Rs. 696.30 - Rs. 660 = Rs. 36.30. The simple interest for one year is Rs. 660 ÷ 2 = Rs. 330. The interest on Rs. 330 for 1 year is Rs. 36.30, so the rate of interest is calculated as (36.30 × 100) ÷ (330 × 1) = 11%. Since 11% is not among the given options, the correct choice is 'None of the above'.