Knowledge Organiser: Percentage Decrease
Part of Percentage Decrease · GCSE GCSE Mathematics revision
This topic summary covers Knowledge Organiser: Percentage Decrease within Percentage Decrease for GCSE Mathematics. Revise Percentage Decrease in Ratio & Proportion for GCSE Mathematics with 12 exam-style questions and 22 flashcards. This topic appears less often, but it can still be a useful differentiator on mixed-topic papers. It is section 6 of 6 in this topic. Use this topic summary to connect the idea to the wider topic before moving on to questions and flashcards.
Topic position
Section 6 of 6
Practice
12 questions
Recall
22 flashcards
Knowledge Organiser: Percentage Decrease
Key Terms
- Percentage decrease: Subtracting a percentage of the original from the original
- Multiplier: The decimal you multiply by to apply the decrease in one step
- Multiplier (decrease): Always less than 1 (e.g. 25% decrease → multiplier = 0.75)
- Depreciation: When an asset (e.g. a car) loses value over time as a percentage
- Key words: discount, reduction, sale, depreciation, fall, decline
Must-Know Facts
- Multiplier for a percentage decrease = 1 - (percentage ÷ 100)
- New amount = original × multiplier
- A 25% decrease means the new amount is 75% of the original
- The multiplier method works in one step — no need to find the decrease separately
- The new amount is ALWAYS smaller than the original for a decrease
Key Formulas
- Multiplier = 1 - (% ÷ 100)
- New amount = original × multiplier
- Decrease amount = original × (% ÷ 100)
- New amount = original - decrease amount
Common Mistakes
- Multiplier > 1: A 20% decrease uses multiplier 0.8, not 1.2 (that's an increase)
- Subtracting % directly: 20% off £60 is NOT £60 − 20 = £40 — find 20% of £60 (= £12) then subtract
- Reverse percentage error: After a 20% decrease to £40, the original is £40 ÷ 0.8 = £50, NOT £40 + 20% of £40
- Successive decreases: Two 10% decreases give 0.9 × 0.9 = 0.81, so a 19% decrease — not 20%
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Practice Questions for Percentage Decrease
What multiplier is used to decrease a value by 35%?
A shop advertises '25% off everything'. A student says: 'The multiplier is 0.25 because 25% = 0.25.' Explain what is wrong with the student's reasoning and state the correct multiplier.
Quick Recall Flashcards
12 questions on Percentage Decrease — practise free
Instant marking, adaptive difficulty, and 22 spaced repetition flashcards. Free until your GCSEs.
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