Find the rate at which a sum of money will double itself in 3 years, if the interest is compounded annually.

Kamala borrowed from Ratan a certain sum at a certain rate for two years simple interest. She lent this sum at the same rate to Harti for two years compound interest. At the end of two years she received Rs. 210 as compound interest, but paid Rs. 200 only as simple interest. Find the sum and the rate of interest.

Find the rate percent per annum, if Rs. 2000 amount to Rs. 2315.25 in an year and a half, interest being compounded six monthly.

Find the rate at which a sum of money will become four times the original amount in 2 years, if the interest is compounded half-yearly.

A certain sum amounts to Rs. 5832 in 2 years at 8% compounded interest. Find the sum.