The value of a machine depreciated by 10% per year during the first two years and 15% per year during the third year. Express the total depreciation of the machine, as percent, during the three years.

Rachna borrows ₹ 12000 at 10 per cent per annum interest compounded half-yearly. She repays ₹ 4000 at the end of every six months. Calculate the third payment she has to make at the end of 18 months in order to clear the entire loan.

During every financial year, the value of a machine depreciates by 12%. Find the original cost of a machine which depreciates by ₹ 2640 during the second financial year of its purchase.

Find the sum on which the difference between the simple interest and the compound interest at the rate of 8% per annum compounded annually be ₹ 64 in 2 years.