Common factors
12 and 18 share some factors.
| 12 factors | 18 factors | Common factors |
|---|---|---|
| 1,2,3,4,6,12 | 1,2,3,6,9,18 | 1,2,3,6 |
Common factors appear in both lists.
Year 6
Identify common factors, common multiples and prime numbers, and use the vocabulary of prime factors and composite numbers
Recognise factors, multiples, primes and composite numbers and use the vocabulary accurately.
Lesson overview
Number - addition, subtraction, multiplication and division
A factor divides exactly into a number. A multiple is found by multiplying. A prime number has exactly two factors: 1 and itself. A composite number has more than two factors.
Prime and composite
13 is prime because only 1 and 13 divide into it. 15 is composite because 1, 3, 5 and 15 divide into it.
Count the factors, not just the number size.
Worked example
What are the common factors of 20 and 30?
| 20 factors | 30 factors |
|---|---|
| 1,2,4,5,10,20 | 1,2,3,5,6,10,15,30 |
- List the factors of 20.
- List the factors of 30.
- Look for numbers that appear in both lists.
- The common factors are 1, 2, 5 and 10.
Try it
Decide whether you are looking for factors or multiples before you begin.
Question 1
Which number is prime?
many factors
1 and 13
1,3,5,15
Question 2
Which is a common factor of 12 and 18?
Question 3
Which is a common multiple of 4 and 6?
Question 4
Which statement is correct?
more than 2 factors
exactly 2 factors
Question 5
Which pair are both multiples of 5?
Common mistakes
Watch for these when working through the lesson.
- Mixing up factors and multiples.
- Calling 1 a prime number.
- Forgetting that a composite number has more than two factors.
Related topics
These ideas fit closely with this lesson.
- Perform mental calculations and use the order of operations.
- Use common factors to simplify fractions.