Supply and demand

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The Law of Demand
The law of demand holds that other things equal, as the price of a good or service rises, its quantity demanded falls.
The reverse is also true: as the price of a good or service falls, its quantity demanded increases.

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Demand Curve
The demand curve has a negative slope, consistent with the law of demand.

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The Law of Supply
The law of supply holds that other things equal, as the price of a good rises, its quantity supplied will rise, and vice versa.
Why do producers produce more output when prices rise?
They seek higher profits
They can cover higher marginal costs of production

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Supply Curve
The supply curve has a positive slope, consistent with the law of supply.

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Equilibrium
In economics, an equilibrium is a situation in which:
there is no inherent tendency to change,
quantity demanded equals quantity supplied, and
the market just clears.

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Equilibrium
Equilibrium occurs at a price of $3 and a quantity of 30 units.

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Shortages and Surpluses
A shortage occurs when quantity demanded exceeds quantity supplied.
A shortage implies the market price is too low.
A surplus occurs when quantity supplied exceeds quantity demanded.
A surplus implies the market price is too high.

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Shift in the Demand Curve
A change in any variable other than price that influences quantity demanded produces a shift in the demand curve or a change in demand.
Factors that shift the demand curve include:
Change in consumer incomes
Population change
Expectations
Consumer preferences
Prices of related goods:
Substitutes: goods consumed in place of one another
Complements: goods consumed jointly

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Shift in the Demand Curve
This demand curve has shifted to the right. Quantity demanded is now higher at any given price.

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Equilibrium After a Demand Shift
The shift in the demand curve moves the market equilibrium from point A to point B, resulting in a higher price and higher quantity.

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Shift in the Supply Curve
A change in any variable other than price that influences quantity supplied produces a shift in the supply curve or a change in supply.
Factors that shift the supply curve include:
Change in input costs
Increase in technology
Change in size of the industry
- Expectations
- Taxes and subsidies
- Prices of related goods

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Shift in the Supply Curve
For an given rental price, quantity supplied is now lower than before.

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Equilibrium After a Supply Shift
The shift in the supply curve moves the market equilibrium from point A to point B, resulting in a higher price and lower quantity.

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Price Ceilings & Floors
A price ceiling is a legal maximum that can be charged for a good.
Results in a shortage of a product
Common examples include apartment rentals and credit cards interest rates and gasoline.
A price floor is a legal minimum that can be charged for a good.
Results in a surplus of a product
Common examples include wheat, milk, minimum wage

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Price Ceiling
A price ceiling is set at $2 resulting in a shortage of 20 units.