Equation Unfold

Two methods, one set of rules, and the switch between them is the lesson. CARRY ACROSS is the quick one: a term does not vanish from one side and appear on the other, it crosses — so it is something you pick up and carry, by dragging or just by tapping it, and the sign turns over IN YOUR HAND the moment you pass the equals sign, before you let go. Drag a coefficient across and the fraction bar is ruled in under the right-hand side while you are still holding it, so the division is something the class watched being made. BOTH SIDES is the slow one, and the reason the first one works: tap a term and the same operation is written on each side at the same instant, then the two on the left are struck out together and cancel. Neither is a different program — the equation ends up in exactly the same state either way, which is the comparison worth putting in front of a class that thinks they are two unrelated tricks. Every line is written left to right in a hand at about the speed a person writes. The arithmetic is never done for them: the equation moves on whatever they type, right or wrong, and nothing is marked until they press Check — carrying a slip two lines and finding it yourself is most of the point. One rule is enforced in both methods, and it is the one worth enforcing: the coefficient will not go until the added number has, because dividing first is how a two-step solve quietly goes wrong. Show me plays the whole solve at the front of the room, a line at a time, in whichever method is selected.