For example, the common factors of 40 and 16 are 2, 4 and 8. The HCF of 40 and 16 is therefore 8. This is the largest number that 'goes into' both numbers. Find the HCF of 12 and 20. The factors ...

but one of the most common is to use a prime factor tree. Firstly, find two numbers that will multiply together to give 40. These are factors of 40. \(4 \times 10 = 40\) would be one way of doing ...