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Finding percentages of amounts is one of the most practical maths skills students learn. This includes calculating discounts, tax, tips, pay rises, and other real-world percentage applications that appear heavily in exam contexts.
Students make these errors again and again. Knowing them in advance gives you a head start.
Calculating the percentage and then forgetting to add or subtract it from the original
Dividing by the new amount instead of the original in reverse percentage problems
Using additive methods that break down for large percentage changes
Insights pulled from Cambridge IGCSE (0580) examiner reports — the exact mistakes candidates make every year.
For train-crossing-bridge problems: (1) Total distance = train length + bridge length, (2) Convert all units to be consistent (all metres + seconds, or all km + hours) BEFORE calculating.
“This was the most challenging question on the paper with less than half of the candidates scoring full marks... Weaker candidates did not attempt a conversion of one or both the units between km and m or hours and seconds. Many combinations of multiplications and divisions of the given values were seen among the weaker candidates.”
Source: CIE 0580 · June 2024 · Paper 2 · Q14
If 5/13 are sold, then 8/13 remain. Set the remainder (96) equal to the remaining fraction (8/13 of total), not the sold fraction. A decimal answer in a whole-number context should alert you to an err
“most candidates not realising that they had to relate the 96 biscuits left to the fraction 8/13 and not to the sold fraction, 5/13. The decimal answers resulting from this error perhaps should have made candidates realise that it had to be incorrect.”
Source: CIE 0580 · June 2021 · Paper 1 · Q13
Percentage profit = (profit / COST PRICE) × 100 — divide by COST, not selling price. Profit = selling − cost. This is the most-missed type of percentage question.
“Calculating the percentage profit proved to be challenging for many candidates. Very few fully correct solutions or part solutions were seen. This was because the majority of candidates divided by the selling price of $24 instead of the cost of $12.80.”
Source: CIE 0580 · November 2021 · Paper 3 · Q1f(i)
Based on 3of 510+ insights extracted from CIE 0580 examiner reports (2018–2024).
This topic is tested by the following exam boards. Our AI tutor covers each one with board-specific content.
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