# What is GCF for 9 and 13?

Nov 3, 2016

GCF of $9$ and $13$ is $1$.

#### Explanation:

The factors of $9$ are $3 \times 3$, and

as $13$ is a prime number, its only factor is $13$.

Note that there are no common factors between them.

Such numbers are called coprimes or relatively primes.

GCF of such numbers is always $1$.

Nov 4, 2016

So GCF (greatest common factor) is 1

#### Explanation:

Using prime numbers as factors: also including 1

color(blue)(ul("Very important fact;")" 1 is not a prime numbers")

$\textcolor{b r o w n}{\text{The only factors of a prime number is 1 and the number itself}}$

$\textcolor{w h i t e}{1} 9 \to \textcolor{red}{1} \times 3 \times 3$
$13 \to \textcolor{red}{1} \textcolor{w h i t e}{\times 3 \times 3} \times 13 \textcolor{b r o w n}{\leftarrow \text{ Thus 13 is a prime number}}$

The only common factor is 1

So GCF (greatest common factor) is 1