Description: Let's get a conceptual understanding of why one needs to divide both sides of an equation to solve for a variable. Created by Sal Khan. And we've got some masses on the left hand side and some masses on the right hand side. We have the same total mass on the left hand side that we have on the right hand side. So you might be tempted to say, well if I could end up with just one mystery mass on the left hand side, and if I keep my scale balanced, then that thing's going to be equal to whatever I have on the right hand side.*Teacher Advisor is 100% free.