This video tutorial shows you the proper way to find the GCF, or greatest common factor. While this is not necessary, the video shows a method of drawing a T chart. List both the numbers that you need to find the GCF, then list there factors, including the number 1. Once you display your factors of both numbers it is a clear cut visual of what the GCF is. In the case of the problem on the video the number 4 has factors of: 1, 2, 4 and the number 20 has factors of: 1, 2, 4, 5, 10, and 20. Therefore the highest factor of both numbers (4), would be your greatest common factor.