Fractions, Decimals & Percentages — 11+ Topic Guide

Part of the GrammarMock topic guides. Read with your child, then drill with the Fractions mini-tests.

Why this topic decides marks

Roughly a quarter of GL maths questions involve fractions, decimals or percentages in some form — either directly ("what is 5/6 of 144?") or hidden inside word problems ("a coat is reduced by 20%..."). It's also the topic Year 5 children most commonly lose marks on, because school coverage varies and the three formats (fraction, decimal, percentage) are really one idea wearing three outfits.

The one idea

A fraction, a decimal and a percentage are three ways to write the same thing:

3/4 = 0.75 = 75%

If your child can move fluently between the three forms, most questions become easy. If they can't, every question is a fresh struggle. So the first two weeks of practice should be conversion drills, not word problems.

Conversions your child should know by heart:

The four question types GL asks

1. Fraction of an amount

"What is 5/8 of 96?"

Method: divide by the bottom, multiply by the top. 96 ÷ 8 = 12, then 12 × 5 = 60.

2. Adding/subtracting fractions

"What is 5/6 − 1/4?"

Method: common denominator first, always. 5/6 = 10/12, 1/4 = 3/12, so 10/12 − 3/12 = 7/12. The exam's wrong-answer options are built from the classic mistake of subtracting tops and bottoms separately (5−1)/(6−4) = 4/2 — teach your child to laugh at that trap.

3. Percentage of an amount

"What is 35% of 240?"

Method: build from 10%. 10% of 240 = 24. So 30% = 72, and 5% = 12. Total 84. The 10% building-block method beats formal multiplication for exam speed every time.

4. Percentage change (the hard one)

"A £60 jacket is reduced to £45. What percentage discount is that?"

Method: change ÷ original × 100. Saving is £15. 15/60 = 1/4 = 25%. The trap: dividing by the NEW price instead of the original. This single error accounts for a big share of lost marks on this question type.

The reverse version is harder still: "After a 30% discount, a coat costs £24.50. What was the original price?" Here £24.50 is 70% of the original, so original = 24.50 ÷ 0.7 = £35. Children want to add 30% back on (£24.50 × 1.3 = £31.85 — wrong). Practise until the "divide by what's left" instinct is automatic.

Common mistakes to drill out

1. Adding denominators (1/4 + 1/4 = 2/8 ✗). It's 2/4 = 1/2.
2. Percentage of wrong base (discount as % of the sale price rather than original).
3. Decimal place slips in ×/÷ by 10, 100 (0.7 × 0.6 = 4.2 ✗; it's 0.42 — count decimal places).
4. Not simplifying (12/16 left as-is when the answer options show 3/4).

Two-week practice plan

• Days 1-4: conversion drills, 10 a day (make flashcards from the table above)
• Days 5-8: fraction-of-amount and percentage-of-amount, 8 questions a day
• Days 9-11: adding/subtracting fractions with different denominators
• Days 12-14: percentage change and reverse percentage word problems

Then take the Fractions mini-test on GrammarMock. 12+/15 = move on. Below that, repeat days 9-14.