Quantity demanded of goods & services at each market price for all prices ceteris paribus. Quantity supplied of goods and services at each market price for all prices ceteris paribus. Note: do not confuse quantity demanded (supplied) at a particular price with demand (supply) which encompasses the quantities demanded (supplied) for all prices. Normal good: demand positively related to income changes. Inferior good: demand negatively related to income changes. Substitute: used in place of another commodity (or factor) Equilibrium: state of rest (no tendency to change) People drive their cars more in the summer and the increased demand for gas increases the price of gas. The increased supply of tomatoes in the summer decreases the price of tomatoes. Problem set #2: demand, supply, and market equilibrium. Could ask the impact on the equilibrium price and quantity of the normal goods and complements in production ,hides and of beef, e. g. , ceteris paribus, given an increase in the income.