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ECON 103

Who gains when prices are controlled?

Move ceilings and floors to see shortages, surplus, actual trade and the gains that disappear. Then solve 10 questions on price controls, welfare and the long run.

Ceilings and access · Step 1 of 12

Compare a maximum price with equilibrium

Willow Bay: price ceiling
Price ($ per unit)
QsQdPcEDₚSₚShortageDSCeiling
Quantity (units)
D; S. Marked point E. Marked point Dₚ. Marked point Sₚ. Shortage. Horizontal Ceiling.
D: demandS: supply
Ceiling: $30E: 30 at $40Dₚ: 35 at $30Sₚ: 20 at $30Shortage: 15
Invented Willow Bay trades glow tiles, with demand P = 100 − 2 × Q and supply P = 10 + 1 × Q. P is dollars per tile and Q is tiles; without a control, the curves meet. A price ceiling is a legal maximum, and it binds only below the free-market price.
Try it: Move the ceiling below, at and above the crossing.
Price ceiling ($ per tile)$30
Free price
$40
Ceiling
$30
Control status
Binding
Demand: P = 100 − 2 × Q. Supply: P = 10 + 1 × Q.
Q* = (100 − 10) ÷ (2 + 1) = 30 units.
P* = (100 − 2 × (30)) = $40.
Compare $30 with $40: The ceiling is below equilibrium price.
Actual price = $30; trade = 20 tiles.
Check yourself
A ceiling exactly at the equilibrium price is…

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