Proportion Balance Lab
Drag the sliders and watch the scale. It balances only when the cross-products match — a × d = b × c — and the lab always reveals the d that would balance.
1 Balance the scale
Four sliders, one rule: the beam sits level exactly when a × d equals b × c. Find the d that balances each setup.
Controls
The scale
2 Recipe scaler
2 eggs make 3 pancakes — a proportion that must stay true at every serving size. Drag the servings and watch both sides scale together.
Controls
Base recipe: 2 eggs and 3 pancakes per serving.