Economics

All else equal, as the price of a good rises, the quantity demanded falls; the demand curve slopes downward.

All else equal, as the price of a good rises, the quantity supplied increases; the supply curve slopes upward.

The price and quantity at which quantity demanded equals quantity supplied, clearing the market with no shortage or surplus.

%ΔQuantity demanded divided by %ΔPrice; it measures responsiveness of quantity demanded to a price change (typically negative).

Demand is elastic when |elasticity| > 1 (quantity very responsive) and inelastic when |elasticity| < 1 (quantity not very responsive); unit elastic equals 1.

%ΔQuantity demanded / %ΔIncome; positive for normal goods, negative for inferior goods.