Microeconomics: Supply, Demand, and Elasticity - Revision Sheet

1. 📌 Essentials

• Demand: Quantity consumers are willing to buy at various prices; inverse relationship with price.
• Supply: Quantity producers willing to sell at various prices; direct relationship with price.
• Price elasticity of demand (PED): Measures responsiveness of quantity demanded to price changes.
• Elastic demand: PED > 1; sensitive to price changes.
• Inelastic demand: PED < 1; less sensitive to price changes.
• Unitary elasticity: PED = 1; proportional change in demand and price.
• Income elasticity (YED): How demand varies with income; positive for normal goods, negative for inferior.
• Cross-price elasticity (XED): Demand change of one good due to price change of another; positive for substitutes, negative for complements.
• Market types: Elastic markets are highly responsive; inelastic markets are less responsive.
• Public goods: Non-rival, non-excludable; provided by government, not profit-driven.
• Demand and supply formulas: QD = 200 - 10P; QS = 50 + 20P (examples).

2. 🧩 Key Structures & Components

• Demand curve — slopes downward; shows quantity demanded at each price.
• Supply curve — slopes upward; shows quantity supplied at each price.
• Elasticity coefficients — numerical measures of responsiveness.
• Market equilibrium — point where demand equals supply.
• Public goods — non-rival, non-excludable; e.g., national defense.
• Substitutes — goods that replace each other (positive XED).
• Complements — goods used together (negative XED).
• Normal goods — demand increases with income.
• Inferior goods — demand decreases with income.
• Advertising — shifts demand curve rightward.
• Price controls — e.g., taxes, subsidies affecting supply/demand.

3. 🔬 Functions, Mechanisms & Relationships

• Demand and supply interact to determine market price and quantity.
• Price elasticity influences how much quantity demanded/supplied responds to price changes.
• Elastic demand: small price change causes large quantity change.
• Inelastic demand: large price change causes small quantity change.
• Income elasticity affects whether a good is normal or inferior.
• Cross-price elasticity indicates substitutability or complementarity.
• Market responsiveness depends on elasticity; elastic markets react strongly, inelastic markets react weakly.
• Advertising shifts demand, influencing equilibrium.
• Public goods are provided when private markets fail due to non-excludability.

4. Comparative Table: Elasticity Types

5. 🗂️ Hierarchical Diagram (ASCII)

Market
 ├─ Demand
 │    ├─ Price effect
 │    └─ Income effect
 ├─ Supply
 │    ├─ Price effect
 │    └─ Production factors
 └─ Equilibrium
      ├─ Price
      └─ Quantity

6. ⚠️ High-Yield Pitfalls & Confusions

• Confusing PED > 1 with PED < 1; remember: elastic > 1, inelastic < 1.
• Assuming all goods are elastic; many necessities are inelastic.
• Misinterpreting cross-price elasticity signs; substitutes are positive, complements are negative.
• Overlooking the difference between income elasticity and price elasticity.
• Ignoring the non-rival, non-excludable nature of public goods.
• Believing elasticity is constant across all price ranges; it varies.
• Forgetting that demand shifts can be caused by advertising, income changes, or prices.
• Confusing market responsiveness with absolute demand/ supply quantities.

7. ✅ Final Exam Checklist

• Understand demand and supply curves and their slopes.
• Know the formulas for PED, YED, and XED.
• Be able to classify goods as elastic, inelastic, or unitary.
• Recognize factors influencing elasticity: availability of substitutes, necessity vs luxury, time horizon.
• Interpret elasticity coefficients and their implications.
• Explain how demand and supply respond to price, income, and cross-price changes.
• Identify market types based on elasticity.
• Describe public goods and their characteristics.
• Understand how advertising shifts demand.
• Be aware of common pitfalls in elasticity interpretation.
• Apply elasticity concepts to real-world market scenarios.
• Calculate changes in demand/supply given elasticity values.
• Recognize the impact of government policies on markets.
• Differentiate between normal and inferior goods based on income elasticity.
• Understand the significance of non-rivalry and non-excludability in public goods.
• Be prepared to analyze shifts and responses in supply and demand graphs.

End of Revision Sheet