On a certain sum of money, compound interest earned at the end of three years is equal to Rs 1456. Compound Interest at the end of two years is Rs 880. Compute the principal invested.

To solve this problem, we need to understand that the difference in compound interest between the third year and the second year is actually the interest on the second year's interest.

Here are the steps to solve this problem:

1. Find the interest for the third year by subtracting the compound interest of the second year from the compound interest of the third year. So, the interest for the third year is Rs 1456 - Rs 880 = Rs 576.

2. This Rs 576 is the interest of the second year's interest. So, the second year's interest is Rs 880.

3. Now, we can find the rate of interest. The formula to calculate the interest is (Interest = Principal * Rate * Time/100). Here, Time is 1 year, Interest is Rs 576 and Principal is Rs 880. If we put these values in the formula, we can calculate the Rate.

   So, 576 = 880 * Rate * 1/100. Solving this equation, we get Rate = (576 * 100) / 880 = 65.45% approximately.

4. Now, we have the rate of interest. We can find the principal of the second year using the formula of interest. We know that the interest of the second year is Rs 880. So,

   880 = Principal * 65.45 * 1/100. Solving this equation, we get Principal = (880 * 100) / 65.45 = Rs 1344.44 approximately.

So, the principal invested was approximately Rs 1344.44.