GCSE Maths Percentages — Multipliers, Change & Exams

GCSE Maths percentages revision

Percentage questions combine number sense with exam wording: 'increase by 15%', 'write as a percentage', 'compare two discounts'. Using multipliers (1.15 for a 15% increase, 0.85 for 15% off) keeps working clean. Reverse percentages (finding original after a change) catch many students — we link to a full percentage-change guide below. Always check whether the answer should be rounded (money to 2 dp, etc.).

Common mistakes in exams

Increasing by 10% then 10% — not the same as 20% total (compound vs additive confusion).

Using the new value as the base for percentage change instead of the original.

Converting between fractions, decimals and percentages inconsistently mid-question.

Rounding before the final step in multi-stage problems.

GCSE Maths: Percentages

Find x% of an amount by multiplying by x/100. Increase by r%: multiply by (1 + r/100). Decrease: multiply by (1 − r/100). Link: percentage change = (change ÷ original) × 100%.

Worked examples

Example 1
Find 15% of £240
0.15 × £240 = £36.
Example 2
Increase £200 by 8%
Multiplier 1.08 → £200 × 1.08 = £216.

Mini quiz (3 questions)

Tap a row to reveal the answer — then start full adaptive practice for instant marking and feedback.

1. A 20% decrease multiplier is:
- A.0.8
- B.1.2
- C.0.2
- D.1.02
Show answer
Correct: 0.8
100% − 20% = 80% of original → ×0.8.
2. If VAT is 20% added to a pre-tax price, the gross multiplier is:
- A.1.2
- B.0.2
- C.1.02
- D.0.8
Show answer
Correct: 1.2
Increase by 20% → ×1.2.
3. Which is 45% as a fraction in simplest form?
- A.9/20
- B.45/100 only
- C.1/2
- D.4/5
Show answer
Correct: 9/20
45/100 = 9/20.

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GCSE Maths percentages revision

Common mistakes in exams