At what simple rate of interest a sum is double in 8 years?

The difference between simple interest and compound on Rs. 1200 for one year at 10% per annum reckoned half-yearly is:

A sum of money lent out at simple interest amounts to ₹720 after 2 years and 1020 after a further period of 5 years. Find the principal. 

A certain sum doubles in 7 years at simple interest. The same sum under the same interest rate will become 4 times in how many years.:

A principal increase by 50 percent in five years at the rate of simple interest. What will be the compound interest for 3 years at Rs 20,000 with the same interest rate?

At what annual percentage rate, 10 years of simple interest on an amount will be $$ {2\over 5}$$ of the addition?

The simple interest on a sum of money for 3 years is ₹240 and the compound interest on the same sum, at the same rate  for 2 years is ₹170. The rate of interest is 

The simple interest on a certain sum of the money at 4 % per annum for 4 years is Rs.80 more than the interest on the same sum for 3 years at 5 % per annum. Find the sum.