GCSE Fractions: Mistakes That Lose Marks in 2026 (Checklist + Examples)

Why fractions matter for GCSE

Fractions appear across multiple GCSE Maths topics: number, algebra, ratio and proportion, probability, and geometry. Losing marks on straightforward fraction operations is one of the most avoidable ways to drop your grade.

This guide targets the specific errors examiners report most often and gives you a practical checklist to use during revision and on exam day.

The GCSE fraction mistakes checklist

Use this checklist before submitting any fraction answer:

• [ ] Did I find the correct common denominator for addition/subtraction?
• [ ] Did I adjust both numerators when changing denominators?
• [ ] Did I simplify my final answer fully?
• [ ] For division, did I flip the correct fraction?
• [ ] Did I convert mixed numbers to improper fractions before calculating?
• [ ] Did I answer in the format the question asks for (fraction, decimal, percentage, mixed number)?
• [ ] Does my answer make sense in context?

Mark-losing mistake 1: Not simplifying

Exam context: The mark scheme awards the final mark only for a fully simplified answer.

Example: Calculate 3/4 + 5/8.

Correct working: 6/8 + 5/8 = 11/8 = 1 3/8.

If a student writes 11/8 and the question says "Give your answer as a mixed number", they lose the final mark.

Fix: Always re-read the question to check the required format. Then simplify.

Mark-losing mistake 2: Arithmetic errors in denominator conversion

Exam context: Multi-mark questions give method marks for correct setup but final marks for correct arithmetic.

Example: Work out 2/3 + 3/5.

Common denominator = 15.

Correct: 10/15 + 9/15 = 19/15 = 1 4/15.

Error: Student writes 2/15 + 3/15 = 5/15 = 1/3. They changed the denominators but not the numerators. They may get a method mark for finding 15 but lose the remaining marks.

Fix: When you multiply the denominator by n, multiply the numerator by the same n.

Mark-losing mistake 3: Division errors

Exam context: Fraction division appears in non-calculator papers and in algebraic fraction questions.

Example: Calculate 4/5 ÷ 2/3.

Correct: 4/5 × 3/2 = 12/10 = 6/5 = 1 1/5.

Common error: Student flips the first fraction: 5/4 × 2/3 = 10/12 = 5/6. Completely wrong answer.

Fix: Keep the first fraction, change the sign, flip the second. See the How to Divide Fractions guide for a full walkthrough.

Mark-losing mistake 4: Mixed number operations without conversion

Exam context: Many GCSE questions involve operations with mixed numbers.

Example: Calculate 2 1/4 × 1 2/3.

Error: Student multiplies 2 × 1 = 2 and 1/4 × 2/3 = 2/12 = 1/6, getting 2 1/6.

Correct: Convert first. 2 1/4 = 9/4, 1 2/3 = 5/3. 9/4 × 5/3 = 45/12 = 15/4 = 3 3/4.

The correct answer is 3 3/4, not 2 1/6. The student loses all marks for the calculation.

Fix: Always convert mixed numbers to improper fractions before doing any operation.

Mark-losing mistake 5: Fraction-decimal-percentage conversion errors

Exam context: Questions that ask you to order values or convert between forms.

Example: Write 3/8 as a percentage.

3 ÷ 8 = 0.375. Then 0.375 × 100 = 37.5%.

Common error: Writing 0.375% (forgetting to multiply by 100) or 3.75% (multiplying by 10 instead of 100).

Fix: Multiply the decimal by 100. Move the decimal point two places to the right.

Exam-style practice questions

Question 1 (3 marks)

Work out 3 1/2 - 1 3/4. Give your answer as a fraction in its simplest form.

Working:

Convert: 3 1/2 = 7/2, 1 3/4 = 7/4.

Common denominator: 7/2 = 14/4.

Subtract: 14/4 - 7/4 = 7/4.

As a mixed number: 1 3/4. As a fraction: 7/4.

The question asks for a fraction (not necessarily a mixed number), and 7/4 is in simplest form (7 is prime).

Answer: 7/4 or 1 3/4 depending on mark scheme expectations.

Question 2 (2 marks)

Calculate 5/6 ÷ 2 1/2. Give your answer as a fraction.

Working:

Convert 2 1/2 = 5/2.

5/6 ÷ 5/2 = 5/6 × 2/5 = 10/30 = 1/3.

Answer: 1/3.

Question 3 (3 marks)

Put these in ascending order: 7/12, 0.6, 58%.

Working:

7/12 = 0.5833...

0.6 = 0.6

58% = 0.58

Order: 0.58, 0.5833..., 0.6

Answer: 58%, 7/12, 0.6.

Question 4 (2 marks)

A bag contains red and blue balls in the ratio 3:5. What fraction of the balls are red?

Working:

Total parts = 3 + 5 = 8.

Fraction of red = 3/8.

Answer: 3/8.

Tips for exam day

1. Show all working. Even if you make an arithmetic error, clear working can earn you method marks.

2. Check the format. If the question says "as a mixed number", do not leave an improper fraction. If it says "simplest form", reduce fully.

3. Estimate first. Before calculating, estimate the rough answer. If 3/4 + 5/8 should be about 1.4, and your answer is 0.4, you know to re-check.

4. Use the checklist. Before moving to the next question, run through the checklist at the top of this guide.

5. Practise under timed conditions. Speed matters. Work through the Worked Examples section with a timer.

For detailed method guides, see How to Add Fractions and How to Divide Fractions.

FAQ

Which GCSE topics involve fractions most heavily? Number operations, algebraic fractions, probability, and ratio/proportion all rely on fraction skills.

Do higher-tier questions have harder fraction content? Yes. Higher tier includes algebraic fractions, recurring decimals as fractions, and multi-step problems that combine several fraction skills.

Can I use a calculator for fraction questions? Some papers are non-calculator. On calculator papers, you can verify answers, but you still need to show method for full marks.

How many marks are typically available for fraction questions? Fraction questions typically carry 2-4 marks each. Across a full GCSE paper, the total fraction-related marks can add up to 15-20.