If an amount doubles automatically in 8 years, then what is the interest rate?

A sum of money at simple interest amount to Rs.4800 in 3 years and Rs.5600 in the 5 years. The sum is

₹ 500 was invested at 12 % per annum simple interest and another certain sum of money invested at 10 % per annum simple interest . If the total interest on both the sum after 4 years is 480, the latter sum of money is

If the simple interest on ₹ 1 for 1 month is 1 paisa, then the rate percent per annum will be 

In what time will the annual simple interest rate at $$ {6{1\over4}{\%}}$$ , 72 rupees becomes 81 rupees?

A sum of ₹ 10,000 is lent partly at 8 % and remaining at 10% per annum. If the yearly interest on the average is 9.2 %, the two parts are 

The simple interest and the true discount on a certain sum for a given period and at a given rate are 25 and 20 respectively. The sum is 

The difference between the compound interest and simple interest of a certain sum of amount is rupees 256.40 for 4 years at 10% rate per annum. Find the sum of money?