1. If a certain principal amount becomes 5 times its original value in 20 years due to interest, then the rate of interest is –

(a) 20% (b) 25% (c) 15% (d) 10%

2. A principal amount doubles in 20 years at a certain simple interest rate. At the same rate of simple interest, the time required for the principal to become three times will be:

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

3. 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.

4. 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)?

5. What should be the annual interest rate (percentage) for a principal amount to become three times its original value in 25 years?

6. At an annual simple interest rate of 8%, how much interest will make the principal amount grow to \(\cfrac{7}{5}\) times its original value?

(a) 4 years (b) 5 years (c) 6 years (d) 7 years

7. 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.

8. At an annual interest rate of \(6\cfrac{2}{3}\%\), determine the time required for the amount to become \(1.5\) times the principal.

9. 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.

10. If a sum of money becomes 4 times its original amount in *n* years at a fixed annual compound interest rate, then in how many years will it become 4 times?

11. What should be the annual compound interest rate for a certain amount of money to become 1.96 times that amount in 2 years?

12. 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.

13. 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?

14. 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?

15. If the compound principal of a certain principal amount after 4 years becomes \(\cfrac{256}{81}\) times the principal, then what is the interest rate?

(a) 15% (b) 30% (c) 33\(\cfrac{1}{3}\)% (d) 25%

16. If a machine's value depreciates at a fixed annual rate and becomes \(\cfrac{1}{2}\) of its original value in 5 years, find the number of years required for its value to become \(\cfrac{1}{4}\) of its original value.

17. If a principal becomes \(3\frac{3}{8}\) times the original amount in 3 years at compound interest, what is the annual rate of interest?