Inverse Proportion
Inverse proportion describes situations where one quantity decreases as the other increases. Students must recognise this relationship, use the formula y = k/x, and solve problems involving inverse square and inverse cube relationships.
Tier
Exam Board
No questions match the current filters for Inverse Proportion.
What You'll Learn
- Recognising inversely proportional relationships
- Setting up and using y = k/x to solve problems
- Working with inverse proportion to powers
- Interpreting inverse proportion graphs (reciprocal curve)
Watch Out For These Mistakes
Students make these errors again and again. Knowing them in advance gives you a head start.
Using direct proportion methods when the relationship is inverse
Forgetting that when x doubles, y halves in inverse proportion
Setting up the formula incorrectly as y = kx instead of y = k/x
What Examiners Say About Inverse Proportion
Insights pulled from Cambridge IGCSE (0580) examiner reports — the exact mistakes candidates make every year.
- Common Mistake●●●●●
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.
Source: CIE 0580 · Feb/March 2024 · Paper 2 · Q14
- Common Mistake●●●●●
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
Source: CIE 0580 · Feb/March 2021 · Paper 1 · Q13
- Misconception●●●●●
Percentage profit = (profit / COST PRICE) × 100 — divide by COST, not selling price. Profit = selling − cost. This is the most-missed type of percentage question.
Source: CIE 0580 · May/June 2021 · Paper 3 · Q1f(i)
Based on 3of 500+ insights extracted from CIE 0580 examiner reports (2018–2024).
Exam Coverage
This topic appears in the Cambridge IGCSE past papers. Our AI tutor can help with it on any question.
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Related Topics
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Ratio, proportion, and percentage formulae