Highest common factors (HCF) The highest common factor (HCF) is the largest number that is a factor of two (or more) other numbers.
Worked example 1 Find the highest common factor (HCF) of 18, 24 and 36.
Solution Method 1
Method 2 Alternatively, we can use the prime factors.
Multiples
A multiple of a number is the number multiplied by another whole number. For example, multiples of 3 are 3, 6, 9, 12, 15, 18 … The lowest common multiple (LCM) is the lowest number that is a multiple of two or more numbers.
Worked example 2 Find the lowest common multiple of 4, 6 and 8.