A man invests ₹ 3,000 for three years at compound interest. After one year, the money amounts to ₹ 3,240. Find the rate of interest and the amount (to the nearest rupee) due at the end of 3 years.

A sum of ₹ 40,000 was lent for one year at 16% per annum. If the same sum is lent for the same time and at the same rate percent but compounded half-yearly, how much more will the interest be ?

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