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Social Studies
Grade 8-12
Supply, Demand & Market Equilibrium Cheat Sheet
A printable reference covering demand, supply, market equilibrium, shortages, surpluses, shifts, and elasticity for grades 8-12.
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Supply and demand explain how buyers and sellers interact in markets. This cheat sheet helps students read market graphs, identify equilibrium, and predict how prices and quantities change. It is useful for class notes, homework, test review, and understanding real-world price changes. The focus is on clear rules, graph interpretation, and common market outcomes.
Key Facts
- The law of demand states that as price rises, quantity demanded falls, and as price falls, quantity demanded rises, all else equal.
- The law of supply states that as price rises, quantity supplied rises, and as price falls, quantity supplied falls, all else equal.
- Market equilibrium occurs where quantity demanded equals quantity supplied, so Qd = Qs.
- A shortage occurs when price is below equilibrium and quantity demanded is greater than quantity supplied, so Qd > Qs.
- A surplus occurs when price is above equilibrium and quantity supplied is greater than quantity demanded, so Qs > Qd.
- A rightward shift of demand increases equilibrium price and equilibrium quantity if supply does not change.
- A rightward shift of supply decreases equilibrium price and increases equilibrium quantity if demand does not change.
- Price elasticity of demand can be estimated as elasticity = percent change in quantity demanded / percent change in price.
Vocabulary
- Demand
- Demand is the quantity of a good or service that consumers are willing and able to buy at different prices.
- Supply
- Supply is the quantity of a good or service that producers are willing and able to sell at different prices.
- Equilibrium Price
- Equilibrium price is the market price where quantity demanded equals quantity supplied.
- Shortage
- A shortage is a market condition where consumers want to buy more than producers are willing to sell at the current price.
- Surplus
- A surplus is a market condition where producers want to sell more than consumers are willing to buy at the current price.
- Elasticity
- Elasticity measures how strongly quantity demanded or supplied responds to a change in price.
Common Mistakes to Avoid
- Confusing a movement along a curve with a shift of the curve is wrong because a price change causes movement, while non-price factors shift the entire curve.
- Labeling the demand curve as upward sloping is wrong because demand usually slopes downward as higher prices lead consumers to buy less.
- Thinking any high price creates a shortage is wrong because a shortage happens when price is below equilibrium, not simply when price feels expensive.
- Forgetting that supply and demand shifts affect both price and quantity is wrong because equilibrium changes in two dimensions on the graph.
- Treating equilibrium as a goal chosen by sellers is wrong because equilibrium is the point where buyers' plans and sellers' plans match in the market.
Practice Questions
- 1 At a price of $6, quantity demanded is 120 units and quantity supplied is 80 units. Is there a shortage or surplus, and how many units is it?
- 2 A market has Qd = 100 - 5P and Qs = 20 + 3P. Find the equilibrium price and quantity.
- 3 If demand for concert tickets increases while supply stays the same, what happens to equilibrium price and equilibrium quantity?
- 4 Explain why a new production technology might lower the market price of a good even if consumer demand does not change.