Prime Factors
Prime factors are the prime numbers that multiply together to make any given number.
What You Need to Know
Key Concept Diagram
A prime number has exactly two factors: 1 and itself (e.g. 2, 3, 5, 7, 11)
Every whole number greater than 1 can be written as a product of prime factors
Factor trees break a number into branches of smaller factors until only primes remain
The prime factorisation of 12 is 2 × 2 × 3, written as 2² × 3
Key Vocabulary
Prime number
A number greater than 1 with no factors other than 1 and itself
Composite number
A number with more than two factors (e.g. 4, 6, 9, 15)
Factor tree
A diagram that breaks a number into factor pairs until all branches are prime
Prime factorisation
Expressing a number as a product of its prime factors
Knowledge Check
Select the correct answer for each question. Click "Check Answer" to see if you are right.
Question 1
Which of the following is a prime number?
Question 2
What is the prime factorisation of 18?
Question 3
How many prime factors does 30 have (counting repeats)?
Key Concepts Summary
- ●A prime number has exactly two factors: 1 and itself (e.g. 2, 3, 5, 7, 11)
- ●Every whole number greater than 1 can be written as a product of prime factors
- ●Factor trees break a number into branches of smaller factors until only primes remain
- ●The prime factorisation of 12 is 2 × 2 × 3, written as 2² × 3