Question

What is the greatest common divisor of 123 and 321?

Answer 1

"Divisor" means the same as "factor."

Answer 2

Factorize each and find the common factors.
We see that 3 is a factor for each number because the sum of digits of each number is divisible by 3.
So start divide each number by three to start factoring:
123=3*41
321=3*107
Since 41 and 107 are both primes, the factoring process is terminated.
Can you see the common factor/divisor now?

Answer 3

or you can use Euclid's algorithm which is incredible!

Answer 4

Yep, I started thinking of using it for 3 digit numbers, unless of course there are obvious factors! Good thinking!