A sum of money doubles itself in 7 years at simple interest. In how much time will it become 5 times of itself?

A person deposited ₹15,600 in a fixed deposit at 10% per annum simple interest. After every second year he adds his interest earned to the principal. The interest at the end of 4 years is:

What is the rate of interest per annum for simple interest at which Rs.880 amounts to Rs.913 in $$1{1\over 2}$$years?

In how much time will a sum of Rs. 12500 amounts to Rs. 20000 at the rate of 8 percent per annum at simple interest?

What will be the ratio of the interests earned by identical sum of money invested at the same rate of simple interest for 6 years and for 15 years respectively?

A sum of money becomes two times of itself in 8 years at simple interest, and it becomes four times of itself in 2 years at compound interest, when interest is compounded annually. Find the ratio of the rate of simple interest to the rate of compound interest offered per year.

Kirti invested a sum of money at a certain rate of simple interest per annum for 3 years in "Bachat scheme". Had she invested the same sum in "Shiksha scheme" for 3 years which has a 2% higher simple interest rate per annum, the investment would have fetched ₹540 more. How much did Kirti invest?

 If 64 amount to 83.20 in 2 years what will ₹ 86 amount to in 4 years at the same rate percent per annum?