Percentage Increase & Decrease
This topic covers 5 learning steps, guiding your child from the basics through to confident problem-solving. Each step includes a worked example and adaptive practice questions.
What Your Child Will Learn
- What Is an Increase?
Understand adding a percentage onto an amount - Calculate Increase
Find the new amount after a percentage increase - Calculate Decrease
Find the new amount after a percentage decrease - Mixed Increase & Decrease
Problems with both increases and decreases - Challenge — Real-World Scenarios
Complex real-world percentage change problems
Common Mistakes
- Thinking that a 20% increase followed by a 20% decrease returns to the original amount
It does not. £100 increased by 20% = £120. Then £120 decreased by 20% = £96, not £100. The decrease is 20% of a BIGGER number. Use real examples to show this. - Adding the percentage to the original instead of calculating the percentage amount first (e.g. £50 increased by 10% = £60 instead of £55)
First calculate the percentage: 10% of £50 = £5. Then add it: £50 + £5 = £55. Alternatively, use the multiplier method: £50 × 1.10 = £55.
Tips for Parents
- Use shopping discounts: "This is £80 with 15% off. What is 10% (£8)? What is 5% (£4)? So 15% off = £12 off. New price = £68."
- Teach the multiplier shortcut: to increase by 20%, multiply by 1.20. To decrease by 20%, multiply by 0.80. This is faster and less error-prone.
- Discuss real-world increases: "Our gas bill went up by 10%. If it was £60, what is it now?" Make percentages meaningful.
- Check understanding by reversing: "After a 25% increase, the price is £50. What was the original price?" This is harder and builds deeper understanding.
Key Words
- Percentage increase — Making an amount bigger by a given percentage — £100 increased by 15% becomes £115.
- Percentage decrease — Making an amount smaller by a given percentage — £100 decreased by 15% becomes £85.
- Multiplier — The number you multiply by — for a 25% increase, the multiplier is 1.25; for a 25% decrease, it is 0.75.
- Original amount — The starting value before any percentage change.
- VAT — Value Added Tax — a percentage added to the price of goods and services (currently 20% in the UK).
Where This Fits
Before this topic: Children should find percentages of amounts confidently and understand what "percent" means.
After this topic: Percentage increase and decrease leads to compound interest, reverse percentages, and proportional reasoning in secondary school.
How MathCraft Teaches This
In MathCraft, Percentage Increase & Decrease is taught through the Number & Fractions adventure track. Your child follows guided lessons with friendly characters, works through examples step by step, then practises with questions that adapt to their level.
The adaptive engine tracks mastery across all 5 steps, revisiting concepts your child finds tricky and advancing when they're ready. Parents can see detailed progress in the Parent Dashboard.
Practise Percentage Increase & Decrease with MathCraft
Step-by-step lessons, worked examples, and adaptive practice — all wrapped in an adventure game your child will love.
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