Understanding the Law of Demand

This lesson explores the Law of Demand: as the price of a good falls, the quantity demanded rises, and vice versa. The graph shows a linear inverse demand curve, P = 20 − 2Q, where Price sits on the vertical axis and Quantity on the horizontal axis.

How to Use the Playground

• Drag the dot along the curve to change Price and Quantity together.
• Use the number field, slider, or +/− buttons (on mobile) — Price and Quantity always stay linked by the equation.
• Watch the Revenue block update live as Revenue = Price × Quantity.
• Try to find the combination that makes Revenue as large as possible.