Question

How many common factors do $9$ and $36$ have?

Answer 1

We know,
$9=3\times 3$
$9=1\times 9$

$\therefore$ Factors of $9$ are $1,3$ and $9.$

Also,
$36=6\times 6$
$36=4\times 9$
$36=3\times 12$
$36=2\times 18$
$36=1\times 36$

$\therefore$ Factors of $36$ are $1,2,3,4,6,9,12,18$ and $36.$

Common factors are $1,3$ and $9.$

Hence, there are $3$ common factors.