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. At an annual simple interest rate of 18%, in how many years will a principal amount become 6 times its original value?

(a) 25 years (b) 30 years (c) 31.78 years (d) 27.78 years

3. 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

4. At what annual interest rate will a principal amount become three times its original value in 25 years?

(a) 6% (b) 8% (c) 10% (d) 12.5%

5. 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

6. If a certain amount of money doubles in \(n\) years under a fixed annual compound interest rate, in how many years will it become 4 times its original value?

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

8. 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?

9. Determine how many years it will take for an amount to become eight times its original value under a fixed annual compound interest rate, given that it doubles in \(n\) years.

10. In compound interest, if an amount becomes \(\cfrac{27}{8}\) times the principal in 3 years, what will be the annual rate of interest? Let me know if you'd like the full solution as well—I'm ready when you are.

11. 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?

12. If a machine’s value depreciates at a fixed annual rate and becomes \(\frac{1}{2}\) of its original value in 5 years, then in how many years will it become \(\frac{1}{4}\) of its original value?

13. If a principal becomes five times through simple interest in 10 years, then in how many years will it become nine times the original amount including interest?

(a) 18 (b) 20 (c) 25 (d) 30

14. At a simple interest rate of \(6\cfrac{1}{4}\%\) per annum, a principal will become three times its original value.

(a) 16 years (b) \(16\cfrac{2}{3}\) years (c) 20 years (d) 32 years

15. 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.

16. Three jars with equal diameter and height were partially filled with dilute sulfuric acid: - the first jar was filled to \(\frac{2}{3}\) of its height, - the second to \(\frac{5}{6}\), and - the third to \(\frac{7}{9}\). If the acid from these three jars is poured into a single jar with a diameter of 2.1 decimetres, and the height of the acid in this jar becomes 4.1 decimetres, then calculate and write the height of each of the original three jars, given that their diameter was 1.4 decimetres.