Question

What is the LCM of 27 and 21?

Answer 1

`LCM = 3xx3xx3xx7 = 189`

Explanation:

YOu can find both the HCF and LCM by writing each number as the product of its prime factors.

The prime factors tell you everything you need to know!

`color(white)(xxxxx)27 = 3xx3xx3`
`color(white)(xxxxx)21 = 3color(white)(xxxxxx)xx7`

`color(white)(xx.)HCF = 3color(white)(xxxxxxxxxxxx) 3" "larr` is the HCF
`color(white)(xx.)LCM = 3xx3xx3xx7 = 189" "larr` is the LCM

To have the LCM, we need a number which contains all the prime factors of the numbers, but without the duplicates.

Use one factor from each column