Greatest common factor of the numbers 12,40 and 60 is

The greatest common factor between any list of numbers is the biggest multiple that they all share.
For example, 5, 35 and 50 all share 5 as the biggest common factor, making 5 the greatest common factor.

Now that we have our example and definition out of the way, let's make out the factors.

12:
1 x 12
2 x 6
3 x 4

40:
1 x 40
2 x 20
4 x 10
5 x 8

60:
1 x 60
2 x 30
3 x 20
4 x 15
5 x 12
6 x 10

Now that we have our factors, let's look for the biggest number that they have in common.

They all share 4 as the biggest number.

Your GCF (Greatest Common Factor) is 4.

I hope this helps!