Writing ratios in simplest form for 11+ maths
21 October 2026
What is a ratio
A ratio compares two or more quantities, showing how much there is of each part in relation to the others.
In 11+ maths, ratios are common in questions about sharing, scaling, and comparing amounts.
Why write ratios in simplest form
Writing a ratio in its simplest form makes it easier to understand and use. It helps to spot patterns and solve problems accurately, which is important in 11+ exams.
Step-by-step example
Let's simplify the ratio 18: 24.
Step 1: Find the highest common factor
Look for the largest number that divides both 18 and 24. This is called the highest common factor (HCF).
Step 2: Work out the HCF
The factors of 18 are 1, 2, 3, 6, 9, 18. The factors of 24 are 1, 2, 3, 4, 6, 8, 12, 24. The highest common factor is 6.
Step 3: Divide both numbers by the HCF
Divide 18 by 6. Divide 24 by 6.
Worked example
18 ÷ 6 = 3
24 ÷ 6 = 4
The simplest form
The ratio 18: 24 in simplest form is 3: 4.
Key insight:
Simplifying ratios helps children solve 11+ maths questions more quickly and with fewer mistakes.
