Question

For two numbers, there exist no common prime factors. Find the GCD of those numbers.

Answer 1

Let's take two arbitrary numbers, and prime factorize them.

$20=2^2\times 5$
$39=3\times 13$

They have no prime factors in common.
However, $1$ is always a factor of every number.

$\therefore$ GCD of such numbers is $1.$