Market clearing and simultaneous changes
導入済み| English | 意味 |
|---|---|
| excess supply/ekˈses səˈplaɪ/ | 過剰供給 |
| market equilibrium/ˈmɑːkɪt ˌiːkwɪˈlɪbrɪəm/ | 市場均衡 |
A decision you can investigate
- A canteen offers meal vouchers. A price set too low creates queues; too high leaves vouchers unsold.
- Equilibrium compares planned buying with planned selling, not total wishes.
Build the explanation
- Equilibrium occurs where quantity demanded equals quantity supplied. Excess demand can encourage price increases; excess supply 超额供给 can encourage price reductions when prices adjust. A demand shift normally changes equilibrium through movement along unchanged supply, and vice versa.
- If both demand and supply rise, quantity normally rises but price depends on their relative shifts. If demand rises while supply falls, price normally rises but quantity is ambiguous. Do not invent a definite result for an unspecified magnitude.
Work through the evidence
- Fictional demand is Qd=120−2P and supply Qs=2P. Set 120−2P=2P: P=30 and Q=60. At P=20, Qd=80 and Qs=40: shortage=40. At P=40, Qd=40 and Qs=80: surplus=40.
- If demand becomes Qd=160−2P with supply unchanged, equilibrium is P=40 and Q=80. If supply also becomes Qs=20+2P, solving gives P=35 and Q=90. Price rises in this specified case, but a larger supply shift could instead lower it.
What is the original equilibrium price?
難易度 1/5 · 100 コイン + 今日初回完了時に小ボーナス付与
120−2P=2P gives 4P=120.
Test the limits
- Adjustment requires prices and production choices to respond. Binding controls, contracts, short production periods or imperfect information can delay clearing. The equations are an illustrative market, not an estimate of canteen behaviour.
- A curve shift is not a move between two points on that curve. Always name which determinant changes and hold the other relevant influences fixed before interpreting a diagram.
What is the shortage at price 20?
難易度 1/5 · 100 コイン + 今日初回完了時に小ボーナス付与
Subtract supply 40 from demand 80.
Higher demand can raise quantity supplied through a movement along an unchanged supply curve.
難易度 1/5 · 100 コイン + 今日初回完了時に小ボーナス付与
True. A demand increase moves the equilibrium along the existing supply curve; the supply curve shifts only when a supply condition changes.
Apply and explain your answer
- Why is the price direction ambiguous when both demand and supply increase without specified magnitudes?
- Demand tends to raise price and supply tends to lower it; the relative shifts determine the net effect.
If demand rises and supply falls, what is normally unambiguous?
難易度 1/5 · 100 コイン + 今日初回完了時に小ボーナス付与
Both changes raise price but have opposing quantity effects.
Use the terms precisely
- market equilibrium 市场均衡: Planned quantity demanded equals planned quantity supplied at a price.
- excess supply: Planned supply exceeds planned demand at a particular price.
Match the terms to their meanings.
難易度 2/5 · 140 コイン + 今日初回完了時に小ボーナス付与
Use each term for its stated economic relationship.
Fictional demand is Qd=120−2P and supply Qs=2P. Set 120−2P=2P: P=30 and Q=60. At P=20, Qd=80 and Qs=40: shortage=40. At P=40, Qd=40 and Qs=80: surplus=40. If demand becomes Qd=160−2P with supply unchanged, equilibrium is P=40 and Q=80. If supply also becomes Qs=20+2P, solving gives P=35 and Q=90. Price rises in this specified case, but a larger supply shift could instead lower it.
Adjustment requires prices and production choices to respond. Binding controls, contracts, short production periods or imperfect information can delay clearing. The equations are an illustrative market, not an estimate of canteen behaviour. A curve shift is not a move between two points on that curve. Always name which determinant changes and hold the other relevant influences fixed before interpreting a diagram.
Equilibrium occurs where quantity demanded equals quantity supplied. Excess demand can encourage price increases; excess supply can encourage price reductions when prices adjust. A demand shift normally changes equilibrium through movement along unchanged supply, and vice versa.
Write from a voucher market
- Demand is Qd = 100 - P and supply is Qs = P.
- Find equilibrium, the shortage at P = 40 and the surplus at P = 60. If both curves shift with no magnitudes, do not state a price direction.
Demand is Qd = 100 - P and supply is Qs = P. Find the equilibrium. Then find the shortage at P = 40 and the surplus at P = 60.
Shortage is excess demand. Surplus is excess supply. Opposite curve shifts need magnitudes before a price prediction.
At P = 40, what imbalance occurs?
難易度 1/5 · 100 コイン + 今日初回完了時に小ボーナス付与
At 40 the planned demand is 60 and planned supply is 40. That is a shortage, not a surplus.