The difference between compound interest and simple interest accrued on an amount of Rs. 18,000 in 2 years is Rs. 405. What is the rate of interest per annum?

The difference between simple interest and compound interest (compounded half-yearly) on a sum at the rate of 25% per annum for 1 year is ₹ 4,375. What is the principal amount?

A person invested half of his capital at 10% simple interest and the other half at 10% compound interest (compounded annually) for 2 years. If the total interest earned is ₹ 4,100, find his total capital.