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

Apr 7, 2016

We first factor each of them into primes:

#### Explanation:

$9 = 3 \times 3$
$18 = 2 \times 3 \times 3$
$21 = 3 \times 7$

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 $7$:

$2 \times 3 \times 3 \times 7 = 126$
$126 \div 9 = 14 = 2 \times 7$
$126 \div 18 = 7$
$126 \div 21 = 6 = 2 \times 3$