Two Scales

Substitution: swap one thing for another

An interactive lesson with 7 steps, about 6 minutes: you predict, drag and solve, with instant feedback on every answer. It runs in your browser and needs JavaScript.

What you’ll learn

• Substitution: if two things are equal, swap one for the other to remove an unknown.
• Elimination: add or subtract whole equations so that one unknown cancels.
• Two unknowns usually need two independent facts (equations).

Steps

1. Boxes and balls
2. Substitution
3. Your turn
4. Another trick: combine the scales
5. Pick the move
6. Tickets
7. Heads and legs