LLL - Number
Factor Trees
Students split a number into factor branches until only prime numbers remain. One question appears on each page.
Year 7
Build numbers into prime branches
Students complete 30 factor-tree questions. The first 5 are guided, then the next 25 practise using the same smallest-prime split method.
Example factor tree
Teaching sequence
Split until the leaves are prime
A factor tree starts with one number. Each branch splits a composite number into two factors. Stop when every branch ends in a prime number.
1. Start with the target number
Write the number at the top. For this lesson, use the smallest prime factor first. If the number is even, start with 2.
2. Keep splitting the composite branch
For 36, write 36 = 2 x 18. Then split 18, because it is still composite.
3. Stop at primes
The tree is finished when the bottom numbers are all prime. For 36, the final leaves are 2, 2, 3, 3.
Classroom method
- Write the number to split.
- Place the smallest prime factor in the left branch.
- Place the remaining factor in the right branch.
- If the right branch is composite, split it again.
- Write the final prime factors across the bottom.
Find the factor tree of 36
Use the smallest prime factor first. Continue until all final leaves are prime.
Summary
Factor tree journal
Progress is recorded for the current browser and, during a live class session, sent to the teacher dashboard.