My ABLE instructor said it has something to do with the number on one side of the equation jumping to the opposite side of the equation and changing its sign to the opposite. Like if it was a positive it will become a negative. (Sounds drastic or like jumping ship) She used it in this math example. I may be able to explain it better when I return to class next week and get some more details.
I found this math web site which is free, if anyone here would want to check it out. It will allow you to view parts of the lessons. But if you sign up, at no cost, you may view the complete lessons.
http://www.brightstorm.com/