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Percentage increase and decrease questions are common on Foundation papers, yet students frequently make simple conversion errors or forget key steps. Below is a typical problem, a clear route through the correct method, and a comparison of where students often go wrong.
Problem
“A coat is marked at £80. The shop applies a 25% discount, then adds 15% VAT to the reduced price. Work out the final selling price.”
| Step | Correct Method | Common Mistake |
|---|---|---|
| 1. Calculate 25% discount | 25% of £80 = 0.25 × 80 = £20, so discounted price = £80 − £20 = £60. | Treating 25% as 25 and computing 80 × 25 = 2000, then dividing wrongly |
| 2. Convert VAT rate | 15% = 0.15 | Using 15 rather than 0.15 |
| 3. Compute VAT on £60 | VAT = 0.15 × 60 = £9, so final price = £60 + £9 = £69. | Adding 15 directly to £60 to get £75, or finding VAT on original £80 |
| 4. State answer | Final selling price = £69. | Omitting the VAT step or forgetting to subtract the discount first |
Common Pitfalls Explained
- Mixing up percentage formats: always convert a percentage to its decimal form (÷100) before multiplying.
- Applying VAT to the original price instead of the discounted price.
- Calculating increase and decrease in the wrong order: discount first, then add VAT.
If you’d like structured practice on combined percentage changes and other Foundation topics, GCSE Maths Tuition can provide step-by-step guidance and exam-style questions to build your confidence.
