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How to work out the HCF and LCM using factor trees - 3 Minute Maths - Free Printable

How to work out the HCF and LCM using factor trees - 3 Minute Maths

Educational worksheet: How to work out the HCF and LCM using factor trees - 3 Minute Maths. Download and print for classroom or home learning activities.

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The image shows two factor trees for the number 42, which is being broken down into its prime factors. Let's analyze both trees and explain the solution.

---

🔍 Understanding Factor Trees



A factor tree is a diagram used to break down a number into its prime factors — that is, the prime numbers that multiply together to give the original number.

We'll go through each tree step by step.

---

🌲 Left Factor Tree:



```
42
/ \
6 7
/ \
2 3
```

- Start with 42
- Break it into 6 × 7
- Then break 6 into 2 × 3
- 7 is already a prime number

So the prime factors are:
2 × 3 × 7

All are prime numbers → this is the prime factorization of 42.

---

🌲 Right Factor Tree:



```
42
/ \
2 21
/ \
3 7
```

- Start with 42
- Break it into 2 × 21
- Then break 21 into 3 × 7
- 2, 3, and 7 are all prime

So the prime factors are:
2 × 3 × 7

Again, same result!

---

Conclusion:



Both factor trees correctly show the prime factorization of 42.

> Prime factorization of 42 = 2 × 3 × 7

Even though the path to get there is different (one starts with 6×7, the other with 2×21), both lead to the same set of prime factors.

This demonstrates that prime factorization is unique (Fundamental Theorem of Arithmetic) — no matter how you split the number, you end up with the same primes.

---

🎯 Final Answer:


$$
\boxed{2 \times 3 \times 7}
$$

This is the prime factorization of 42, confirmed by both factor trees.
Parent Tip: Review the logic above to help your child master the concept of lcm factor tree worksheet.
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