11 plus maths practice for least common multiple and greatest common divisor
26 October 2026
11 plus maths practice for least common multiple and greatest common divisor
Understanding LCM and GCD is key for 11+ maths exams. These skills help with fractions, ratios and problem solving in both CEM and GL exam styles.
What are LCM and GCD
LCM stands for Least Common Multiple. It is the smallest number that is a multiple of two or more numbers.
GCD, also called Greatest Common Divisor or Highest Common Factor (HCF), is the largest number that divides two or more numbers exactly.
Why these skills matter
Questions on LCM and GCD appear in many 11+ maths papers. Knowing how to find them helps children solve word problems, compare fractions, and check answers with confidence.
Worked example
Find the LCM and GCD of 12 and 18.
Step 1: Find the prime factors of 12: 2 × 2 × 3.
Step 2: Find the prime factors of 18: 2 × 3 × 3.
Step 3: For GCD, take the common factors: 2 × 3 = 6.
Step 4: For LCM, use all the factors with the highest powers: 2 × 2 × 3 × 3 = 36.
The GCD of 12 and 18 is 6, and the LCM is 36.
Key insight: Practising LCM and GCD with your child builds number sense and makes fraction and ratio problems much easier to tackle.
Tips for supporting at home
Encourage your child to list multiples for LCM and use factor trees for GCD. Talk through each step and check answers together. This helps build confidence and accuracy for 11+ exams.
