The population of a town decreased by 12% during 1998 and then increased by 8% during 1999. Find the population of the town, at the beginning of 1998, if at the end of 1999 its population was 285120.

A sum of money, invested at compound interest, amounts to ₹ 16500 in 1 year and to ₹ 19965 in 3 years. Find the rate per cent and the original sum of money invested.

A sum of money lent out at C.I. at a certain rate per annum becomes three times of itself in 10 years. Find in how many years will the money become twenty-seven times of itself at the same rate of interest p.a.

Mr. Sharma borrowed a certain sum of money at 10% per annum compounded annually. If by paying ₹ 19360 at the end of second year and ₹ 31944 at the end of the third year he clears the debt; find the sum borrowed by him.