1. A certain sum of money amounts to ₹944 in 3 years at simple interest. If the rate of interest is increased by 25%, the same sum amounts to ₹980 in the same time period. Find the principal amount and the original rate of interest.

2. Determine the principal and the annual simple interest rate if a sum of money amounts to ₹7100 in 7 years and ₹6200 in 4 years at the same annual rate of simple interest.

3. The simple interest for 2 years and the compound interest for 1 year (with annual compounding) on the same principal at the same rate are ₹800 and ₹820 respectively. Find the principal and the rate of interest.

4. If a principal amount yields a total of ₹7,100 (principal + simple interest) in 7 years and ₹6,200 in 4 years at the same annual rate of simple interest, find the principal and the annual rate of simple interest.

5. If the difference between the compound interest and the simple interest on a certain sum of money for 2 years at an annual interest rate of 9% is ₹129.60, then find the principal amount.

6. Mannan Miah saw that after 6 years of borrowing a sum of money, the amount of simple interest had become \(\frac{3}{8}\) of the principal. Determine the annual rate of simple interest.

7. A certain principal doubles in 20 years at a given rate of simple interest. At the same rate of simple interest, that principal will become triple in —

(a) 30 years (b) 35 years (c) 40 years (d) 45 years

8. Some money amounts to 944 rupees in 3 years at simple interest. If the annual rate of interest increases by 25%, then the same money amounts to 980 rupees in the same time. Find the rate of interest and the principal.

9. If a certain amount of money triples in 20 years, then at the same simple interest rate, in how many years will it double?

10. Some money becomes 5 times its original amount in 5 years at simple interest. At the same rate of interest, the time required for that principal to become 17 times is:

(a) 17 years (b) 20 years (c) 18 years (d) 19 years

11. Uday Babu lent a certain amount of money to one person at an annual simple interest rate of 4% for 4 years, and twice that amount to another person at an annual simple interest rate of 10% for the same duration. He received ₹960 more interest from the second person than from the first. Find the total amount of money Uday Babu lent.

12. A farmer deposited some money in the village post office. After 4 years, he found that the total amount including interest had become ₹434. He calculated that the interest he received was \(\frac{6}{25}\) of his principal amount. Find how much money he had originally deposited and what annual rate of simple interest the post office gave.

13. Bimal Babu lent a certain amount of money to one person at an annual simple interest rate of 8% for 4 years, and twice that amount to another person at an annual simple interest rate of 10% for the same duration. Bimal Babu received ₹960 more interest from the second person than from the first. Find the total amount of money Bimal Babu lent.

14. The simple interest and compound interest on a certain principal for 2 years are ₹4,000 and ₹4,100 respectively. Find the principal and the rate of interest.

15. ₹1200 is deposited for 4 years and ₹2000 for 3 years in a bank at the same rate of simple interest. If the total interest earned is ₹594, what is the annual rate of interest (percentage)?

16. The simple interest on ₹400 for 5 years and on ₹600 for 4 years together amounts to ₹132. If the rate of interest is the same in both cases, find the rate of interest.

(a) 3% (b) 5% (c) 7% (d) 9%

17. What should be the annual rate of simple interest (in percent) so that the interest on a sum of money for 10 years becomes \(\frac{2}{5}\) of the total amount (principal + interest)?

18. If a certain principal amount amounts to ₹1248 in 7 years and ₹1056 in 4 years at the same annual rate of simple interest, find the principal and the annual rate of simple interest.

19. When Mr. Subir retired from his job, he received a lump sum of ₹6,00,000 from his Provident Fund and Gratuity. He wants to divide this amount between the post office and the bank in such a way that he earns ₹34,000 annually as interest. If the annual simple interest rates of the post office and the bank are 6% and 5% respectively, determine how much money he should deposit in each.

20. If a certain principal earns ₹560 in 3 years and ₹600 in 5 years at the same annual simple interest rate, find the amount of the principal and the annual rate of simple interest.

21. If the difference between the compound interest and simple interest on a certain sum of money for 3 years at an annual rate of 10% is ₹930, then what is the amount of that sum?

22. What should be the annual simple interest rate (in percentage) so that the interest on a sum of money for 6 years becomes \(\frac{18}{25}\) of the principal?

23. Mr. Bimal deposited ₹5,600 in a bank at a simple interest rate of 10% for his 13-year-old son and 15-year-old daughter in such a way that when both turn 18 years old, they each receive the same amount including interest. How much money did he deposit separately for his son and daughter?

24. If the simple interest on a certain principal for 2 years at an annual rate of 15% is ₹160, find the compound interest.

(a) ₹ 205 (b) ₹ 172 (c) ₹ 200 (d) none of the above

25. If the difference between the compound interest and simple interest on a certain sum at a rate of 20% per annum for 3 years is ₹800, what is the principal amount?

(a) ₹ 5250 (b) ₹ 8650 (c) ₹ 6250 (d) none of the above

26. Rekha deposited ₹10,000 of her savings into two separate banks. One bank offers an annual simple interest rate of 6%, while the other offers 7%. After 2 years, she receives ₹1,280 as interest. How much money did she deposit in each bank?

27. Write down the calculation to determine in how many years a sum of money will double at an annual simple interest rate of 6%.

28. At the same time, Amal Ray deposited ₹2000 in a bank and Pashupati Ghosh deposited ₹2000 in a post office. After 3 years, they received ₹2360 and ₹2480 respectively, including interest. Calculate and write the ratio of the annual simple interest rates of the bank and the post office.

29. Mr. Rathin deposits money in the bank for each of his two daughters in such a way that when each daughter turns 18 years old, she will receive ₹120000. The bank offers simple interest at an annual rate of 10%. The current ages of the daughters are 13 years and 8 years respectively. Calculate how much Mr. Rathin deposited in the bank for each daughter.

30. If a certain principal amount yields a total of ₹7,400 in simple interest after 4 years at an annual rate, and another total of ₹6,200 in simple interest after 4 years, calculate the principal and the annual rate of simple interest.