Equilibrium price and quantity from changes in both supply and demand

Overview of Supply and Demand Dynamics

1. Introduction to Curve Movements

  • Context: Understanding shifts in supply and demand curves and their effects on equilibrium price and quantity.

2. Scenario 1: Supply Increases & Demand Decreases

  • Situation Explanation:
    • Major producer enters the market (causing supply to increase).
    • New study indicates ice cream is less healthy than previously thought (causing demand to decrease).
  • Effects on Curves:
    • Supply Curve (S):
    • Shifts to the right (increases supply).
    • New supply curve depicted as S2.
    • Demand Curve (D):
    • Shifts to the left (decreases demand).
    • New demand curve depicted as D2.
  • Equilibrium Analysis:
    • Equilibrium Price:
    • Unambiguous decrease due to increased competition among suppliers and decreased demand. Price moves down.
    • Equilibrium Quantity:
    • Indeterminate: Shift could result in:
      • Quantity remains the same.
      • Quantity increases slightly.
      • Quantity decreases slightly.

3. Scenario 2: Supply Decreases & Demand Increases

  • Situation Explanation:
    • Factors causing supply to decrease (e.g., production costs rise).
    • Factors causing demand to increase (e.g., rising popularity of ice cream).
  • Effects on Curves:
    • Supply Curve (S):
    • Shifts to the left and up (decreases supply).
    • New supply curve designated as S2.
    • Demand Curve (D):
    • Shifts to the right and up (increases demand).
    • New demand curve designated as D2.
  • Equilibrium Analysis:
    • Equilibrium Price:
    • Unambiguously increases because of decreased supply alongside greater demand.
    • Equilibrium Quantity:
    • Indeterminate: Potential outcomes based on exact curves:
      • Quantity increases slightly.
      • Quantity remains the same.
      • Quantity decreases slightly.

4. Scenario 3: Both Supply and Demand Increase

  • Situation Explanation:
    • Factors causing both supply and demand to increase (e.g., successful marketing efforts and lower production costs).
  • Effects on Curves:
    • Supply Curve (S):
    • Shifts to the right and down (increases supply).
    • Demand Curve (D):
    • Shifts to the right and up (increases demand).
  • Equilibrium Analysis:
    • Equilibrium Quantity:
    • Unambiguously increases with both curves moving in favor of a higher quantity.
    • Equilibrium Price:
    • Ambiguous: It could:
      • Remain the same.
      • Increase.
      • Decrease, depending on the relative magnitude of supply and demand shifts.

5. Scenario 4: Both Supply and Demand Decrease

  • Situation Explanation:
    • Factors causing both supply and demand to decrease (e.g., economic downturn or new regulations).
  • Effects on Curves:
    • Supply Curve (S):
    • Shifts to the left and up (decreases supply).
    • Demand Curve (D):
    • Shifts to the left and down (decreases demand).
  • Equilibrium Analysis:
    • Equilibrium Quantity:
    • Unambiguously decreases as both curves shift negatively, indicating lower demand and supply.
    • Equilibrium Price:
    • Ambiguous: Price could:
      • Remain unchanged.
      • Increase.
      • Decrease depending on the specific shapes and magnitudes of the shifts.

6. Importance of Labeling in Diagrams

  • Key Points:
    • Remember to label curves, equilibrium prices (P), and quantities (Q).
    • Make sure to denote shifts clearly with arrows in graphs.
    • For exams (such as AP exams), emphasize clarity and accuracy in graphs and explanations.