IGCSE Mathematics: Percentages Practice Questions
To increase a value by a percentage, multiply by a multiplier greater than 1. To reverse a percentage change, divide by the multiplier rather than applying the percentage again.
Topic 1.13 of Cambridge IGCSE Mathematics 0580 appears on every paper, and reverse percentages are where marks are lost. The multiplier method handles increases, decreases, compound growth and reversals with one idea. The questions below use it throughout.
What you need to know for Percentages
- MultiplierAn increase of 15 per cent uses a multiplier of 1.15. A decrease of 20 per cent uses 0.8. Add or subtract the percentage from 100, then divide by 100.
- Percentage changeChange divided by the original amount, multiplied by 100. The original always goes on the bottom.
- Reverse percentageWhen the given value is the result of a change, divide by the multiplier to find the original. Do not subtract the percentage from the new value.
- Compound interestFinal amount = principal x multiplier raised to the power of the number of periods. Interest earned is the final amount minus the principal.
- DepreciationCompound decrease. Use a multiplier below 1 raised to the number of years.
- Simple interestInterest = principal x rate x time, divided by 100. The interest is the same every year, unlike compound interest.
IGCSE Mathematics Percentages questions and answers
4 exam-style questions written to the 0580 syllabus. Try each one on paper first, then open the worked answer to check your method against the marks.
Increase 240 by 15 per cent.
Show the worked answer
- Find the multiplier for a 15 per cent increase: 100 + 15 = 115, so the multiplier is 1.15.
- Multiply the original amount by the multiplier: 240 x 1.15.
- 240 x 1.15 = 276.
- As a check, 10 per cent of 240 is 24 and 5 per cent is 12, so the increase is 36, and 240 + 36 = 276.
A jacket is reduced by 20 per cent in a sale and now costs RM96. Calculate its original price.
Show the worked answer
- A 20 per cent decrease means the sale price is 80 per cent of the original, so the multiplier is 0.8.
- Original x 0.8 = 96.
- To reverse the change, divide rather than multiply: original = 96 divided by 0.8.
- Original = RM120. Check: 20 per cent of 120 is 24, and 120 minus 24 = 96.
RM5000 is invested at 4 per cent per year compound interest. Calculate the total interest earned after 3 years, correct to the nearest ringgit.
Show the worked answer
- The multiplier for a 4 per cent increase is 1.04, applied once for each year.
- Final amount = 5000 x 1.043.
- 1.043 = 1.124864, so the final amount is 5000 x 1.124864 = RM5624.32.
- The interest earned is the final amount minus the original: 5624.32 minus 5000 = RM624.32, which is RM624 to the nearest ringgit.
A shop's daily sales rise from 45 items to 54 items. Calculate the percentage increase.
Show the worked answer
- Find the change: 54 minus 45 = 9 items.
- Percentage change = change divided by the original, multiplied by 100. The original is 45.
- 9 divided by 45 = 0.2.
- 0.2 x 100 = 20 per cent increase.
Common mistakes in this topic
- Reversing a percentage by applying it again to the new value.
- Dividing by the new amount instead of the original in a percentage change.
- Giving the final amount when the question asks for the interest.
- Using simple interest when the question says compound.
- Multiplying by 0.15 rather than 1.15 for a 15 per cent increase.
Exam tips
- Convert every percentage to a multiplier before calculating. One method then covers increases, decreases and compound growth.
- The word original, before or was signals a reverse percentage, which means divide.
- For compound interest, the power equals the number of years, not the number of years plus one.
- Read whether the answer wanted is the final amount or the change.
- Sense check: an increase must give a larger answer, a decrease a smaller one.
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Percentages FAQs
What is a reverse percentage?
It is a calculation where the value you are given is the result of a percentage change and you need the original. Work out the multiplier for the change, then divide the given value by it. Subtracting the percentage from the new value gives the wrong answer.
How do I calculate compound interest?
Multiply the principal by the multiplier raised to the power of the number of periods. For 4 per cent over 3 years, multiply by 1.04 cubed. Subtract the principal from the result if the question asks for the interest earned rather than the final amount.
How do I find a percentage change?
Divide the change by the original amount, then multiply by 100. The original value always goes on the bottom, whether the change is an increase or a decrease. Dividing by the new value is the most common error in this topic.
What is the difference between simple and compound interest?
Simple interest is calculated on the original principal each year, so the same amount is added annually. Compound interest is calculated on the growing balance, so each year's interest is larger than the last and the total grows faster.
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Written to the published Cambridge IGCSE Mathematics (0580) syllabus. Check your school entry code and syllabus year, because Core and Extended candidates are assessed on different content. Last reviewed 2026-08-12.