Question

What is the least common multiple of 9, 18 , and 21?

Answer 1

We first factor each of them into primes:

Explanation:

`9=3xx3`
`18=2xx3xx3`
`21=3xx7`

Now we take all prime factors to their highest degree that we find in the numbers, so we have one `2`, two `3`'s and one `7`:

Answer:
`2xx3xx3xx7=126`

Check :
`126div9=14=2xx7`
`126div18=7`
`126div21=6=2xx3`
And there is no common factor between the three of them.