Practice Percentage and interest calculations
Interest calculations relate an amount of money, an interest rate and a time period.
Simple interest and compound interest use different rules, so always check the conditions.
Exercises with solutions
Interest is calculated with Z = (K · p · t) ÷ 100, where K is the capital, p the interest rate in percent and t the time in years. For months use t = months ÷ 12. The final amount is the capital plus the interest.
Exercise 1
Calculate the interest on €800 at 3 % for one year.
Show solution and working
€24
Z = (800 · 3 · 1) ÷ 100 = 2400 ÷ 100 = 24.
Exercise 2
Calculate the interest on €1,200 at 2 % for two years.
Show solution and working
€48
Z = (1200 · 2 · 2) ÷ 100 = 4800 ÷ 100 = 48.
Exercise 3
What is the final amount for €500 at 4 % for one year?
Show solution and working
€520
Interest: (500 · 4) ÷ 100 = €20. Final amount: €500 + €20 = €520.
Exercise 4
Calculate the interest on €900 at 4 % for half a year.
Show solution and working
€18
Half a year means t = 0.5. Z = (900 · 4 · 0.5) ÷ 100 = 1800 ÷ 100 = 18.
Common mistake
Confusing the interest rate with the interest. The rate is the percentage (3 %), the interest is the amount of money (€24). And always insert the time in years, so divide months by 12.
Keep learning with MatheJump
Create a free account and explore math practice. Choose from the available exercises to suit your learning needs.