Breaking down into prime factors
You learn to split a composite number into a multiplication of prime numbers.
How to work it out
- Write a number as a product of prime numbers (2, 3, 5, 7).
- Divide each time by the smallest prime that goes into it until you get to 1.
112 = 2 × 622 × 6 = 2 × 2 × 3
Factorise 12
- Divide 12 by the smallest prime number: 12 ÷ 2 = 6.
- Divide 6 by 2 again: 6 ÷ 2 = 3.
- The number 3 is already prime.
- The prime factors are 2 × 2 × 3 = 12.
More examples
20 = 2 × 2 × ?
- Multiply the known factors: 2 × 2 = 4.
- Divide the number by 4: 20 ÷ 4 = 5.
- The missing prime factor is 5.
12 × 2 = 4220 : 4 = 5
18 = 2 × 3 × ?
- Work out the known factors: 2 × 3 = 6.
- Divide 18 by 6: 18 ÷ 6 = 3.
- The missing prime factor is 3.
12 × 3 = 6218 : 6 = 3