The GCF is 64.
The GCF of 280 and 320 is 40
The GCF of 320 and 840 is 40.
20
Since 20 is a factor of 320, it is automatically the GCF.
5
Since 40 is a factor of 320, it is automatically the GCF.
Well, honey, the highest common factor of 320 and 128 is 64. You see, 64 is the largest number that can divide both 320 and 128 without leaving a remainder. So there you have it, 64 is the boss in this situation.
The GCF is 10.
The GCF is 80.
The GCF is 16.
The GCF is 5.