Compound Interest - General Questions

A sum of money doubles itself at compound interest in 6 years. In how many years will it become four times?

A sum amounts to Rs. 7,400 in 2 years and to Rs. 8,880 in 3 years at compound interest. What is the rate of interest?

The difference between compound interest and simple interest on a certain sum at 12% per annum for 2 years is Rs. 8.64. What is the sum?

What is the compound interest on Rs. 22,800 at 15% per annum for 2 years, compounded annually?

Find the amount on Rs. 12,000 for 3 years at 10% per annum compounded annually.