How to explain find the lcm in lcm and hcf to your child
27 October 2026
When your child is learning about LCM and HCF, it helps to see a clear example. Breaking the process into steps makes it much easier for children to follow and understand.
Example question
Find the least common multiple (LCM) of 12 and 18.
Step 1: Write each number as a product of prime numbers.
12 = 2 × 2 × 3
18 = 2 × 3 × 3
Step 2: Find all the prime numbers that appear, using the highest number of times each appears in either number.
For 2: the highest is two times (from 12).
For 3: the highest is two times (from 18).
Step 3: Multiply these together to get the LCM. LCM = 2 × 2 × 3 × 3 = 36
The least common multiple of 12 and 18 is 36.
| Number | Prime Factors |
|---|---|
| 12 | 2 × 2 × 3 |
| 18 | 2 × 3 × 3 |
Now your child can spot the prime factors in each number and combine them to find the least common multiple. This builds confidence for similar questions, and there are more practice problems just like this to help them get ready for the 11+.
