The only common factor is 1.
The GCF is 12.
1 and 3
It is: 4
It is 1
You are 12-20. The only common factor of 11 and 21 is 1.
3 is a factor of 12 & a factor of 15, so it's a common factor between 12 & 15. Also, as it's the only common factor between them, in addition to 1 of course, it's the highest common factor between 12 & 15.
12
12?
The GCF is 12.
The greatest common factor between the two is 12.
The least common factor of any set of integers is 1.
4.
It is: 12
It is 1
It is: 4
It is 4
1 and 3