How to find the greatest common factor of 24, 28?

You could discover the prime factors of ${\displaystyle 24}$ and ${\displaystyle 28}$.

${\displaystyle 24=2^2\cdot 3}$
${\displaystyle 28=2^2\cdot 7}$

We see that ${\displaystyle 24}$ and ${\displaystyle 28}$ have ${\displaystyle 2^2}$ in common and nothing else, so the greatest common factor is

${\displaystyle 2^2=4}$

There are other ways to find the GCF as well such as listing out all the factors of each number and picking out the greatest, which is a little more tedious and unnecessary.