Answer :
Because one of the numbers can be prime numbers, for example the greatest common factor of 12 and 13 it's 1 because 13 it's a prime number or because they don't have common prime factors.Prime numbers are the numbers who can be divided just by 1 and themselves.
Step-by-step explanation:
The greatest common factor of two numbers is sometimes 1 when they are coprime to each other.
Coprime numbers are those numbers who are relatively prime.
Now, prime numbers are those numbers who are divisible by 1 and itself only.
So, eventually when we going to find the greatest common factor of two prime numbers it comes out to be 1 only.
For example, we takes two numbers 2 and 5 ,
Factor of 2 = 1,2
Factor of 5= 1,5
So , 1 is only common factor between them.
