A sum of money becomes 4 times at simple interest in 10 years. What is the rate of interest?

A took a certain sum as loan from bank at a rate of 8 % Simple Interest per annum. A lends the same amount to B at 12 % Simple interest per annum. If at the end of the five years. A made profit of Rs 800 form the deal, how much was the original sum? 

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?

Mr. Khanna took a loan of Rs 10,000 on simple interest for two years at the rate 3% per annum. The total amount that he will be paying as interest in 2 year is 3% of his monthly salary. What his monthly salary?

A sum of money becomes triple itself in 16 years. In how many years will it become 5 times at the same rate?

A sum is to be paid back in 3 equal annual instalments. The interest is compound annually at 30% per annum. If each instalment be Rs.21970 then what is the sum?

In what time will the simple interest be 2/5 of the principal at 8 percent per annum?