The simple interest on a certain sum of money for 2 years at 7% per annum is double the compound interest on ₹1,000 for 2 years at 10% per annum, compounded annually. What is the sum placed on simple interest?

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.