Four factors in common.
Four common factors.
The common factors are: 1, 2, 3, 6.
The four common factors are: 1, 3, 17, 51.
The factors of 18 are 1,2,3,6,9 and 18. For them to be common, they need to be compared to another set of factors.
There are only two common factors for 56 and 21. They are 1 and 7.
The common factors are: 1, 2, 4, 8, 16
2 and 1
2
It is four.
Four of them.
The greatest common factor is four.