11+ Maths: Writing Ratios in Simplest Form (GL & CEM style)
19 October 2026
What is a ratio
A ratio is a way to compare quantities. For example, if a fruit bowl has 4 apples and 6 oranges, the ratio of apples to oranges is 4:6. Ratios show how much of one thing there is compared to another.
Ways to write ratios
Ratios can be written using the word 'to' (4 to 6), a colon (4:6), or as a fraction (4/6). The colon is the most common form in 11+ questions.
Simplifying ratios step by step
To write a ratio in its simplest form, divide all parts by their highest common factor (HCF). For 4:6, the HCF is 2. Divide both numbers by 2: 4 ÷ 2 = 2 and 6 ÷ 2 = 3, so the simplest form is 2:3.
Three-part ratios
Sometimes, ratios have more than two parts. For example, 12:18:6. Find the HCF (which is 6), then divide each part: 12 ÷ 6 = 2, 18 ÷ 6 = 3, 6 ÷ 6 = 1. The simplest form is 2:3:1.
Converting units before writing ratios
If the quantities use different units, convert them to the same unit first. For example, if you have 500g and 2kg, change 2kg to 2000g. Now write the ratio as 500:2000 and simplify to 1:4.
Key insight: Encourage your child to look for the largest number that divides all parts of the ratio. This helps avoid extra steps and keeps the process calm and efficient.
