Transcript Chapter 2
Chapter 2
The Basics of Supply and
Demand
Introduction
What are supply and demand?
What is the market mechanism?
What are the effects of changes in
market equilibrium?
What are elasticities of supply and
demand?
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Topics to Be Discussed
How do short-run and long-run
elasticities differ?
How do we understand and predict the
effects of changing market conditions?
What are the effects of government
intervention – price controls?
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Supply and Demand
Supply and demand analysis can:
1. Help us understand and predict how world
economic conditions affect market price and
production
2. Analyze the impact of government price
controls, minimum wages, price supports,
and production incentives on the economy
3. Determine how taxes, subsidies, tariffs and
import quotas affect consumers and
producers
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Supply and Demand
The Supply Curve
The relationship between the quantity of a
good that producers are willing to sell and the
price of the good.
Measures quantity on the x-axis and price on
the y-axis
Q S Q S (P)
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The Supply Curve
S
Price
($ per unit)
The Supply
Curve Graphically
P2
The supply curve slopes
upward demonstrating that
at higher prices firms
will increase output
P1
Q1
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The Supply Curve
Change in Quantity Supplied
Movement along the curve caused by a
change in price
Change in Supply
Shift of the curve caused by a change in
something other than price
Change
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in costs of production
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Change in Supply
Other Variables Affecting Supply
Costs of Production
Labor
Capital
Raw
Materials
Lower costs of production allow a firm to
produce more at each price and vice versa
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Change in Supply
The cost of raw
materials falls
Produced Q1 at P1
and Q0 at P2
Now produce Q2 at
P1 and Q1 at P2
Supply curve shifts
right to S’
P
S
P1
P2
Q0
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S’
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Q1
Q2
Q
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Supply and Demand
The Demand Curve
The relationship between the quantity of a
good that consumers are willing to buy and
the price of the good.
Measures quantity on the x-axis and price on
the y-axis
QD QD(P)
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The Demand Curve
Price
($ per unit)
The demand curve slopes
downward demonstrating
that consumers are willing
to buy more at a lower price
as the product becomes
relatively cheaper.
P2
P1
D
Q1
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The Demand Curve
Changes in quantity demanded
Movements along the demand curve caused
by a change in price.
Changes in demand
A shift of the entire demand curve caused by
something other than price.
Income
Preferences
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Change in Demand
Other Variables Affecting Demand
Income
Increases
in income allow consumers to
purchase more at all prices
Consumer Tastes
Price of Related Goods
Substitutes
Complements
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Change in Demand
Income Increases
P
D
D’
Purchased Q0, at P2
P2
and Q1 at P1
Now purchased Q1 at
P2 and Q2 at P1
Same for all prices P1
Demand Curve shifts
right
Q0
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Q1
Q2
Q
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The Market Mechanism
The market mechanism is the tendency
in a free market for price to change until
the market clears
Markets clear when quantity demanded
equals quantity supplied at the prevailing
price
Market Clearing price – price at which
markets clear
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The Market Mechanism
S
Price
($ per unit)
The curves intersect at
equilibrium, or marketclearing, price.
Quantity demanded
equals quantity
supplied at P0
P0
D
Q0
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The Market Mechanism
In equilibrium
There is no shortage or excess demand
There is no surplus or excess supply
Quantity supplied equals quantity demanded
Anyone who wished to buy at the current
price can and all producers who wish to sell
at that price can
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Market Surplus
The market price is above equilibrium
There is excess supply - surplus
Downward pressure on price
Quantity demanded increases and quantity
supplied decreases
The market adjusts until new equilibrium is
reached
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The Market Mechanism
Price
($ per unit)
S
1.
Surplus
P1
2.
3.
P0
4.
D
Q
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D
Q0
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QS
Price is above
the market
clearing price –
P1
Qs > QD
Price falls to
the marketclearing price
Market adjusts
to equilibrium
Quantity
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The Market Mechanism
The market price is below equilibrium:
There is a excess demand - shortage
Upward pressure on prices
Quantity demanded decreases and quantity
supplied increases
The market adjusts until the new equilibrium
is reached.
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The Market Mechanism
Price
($ per unit)
1.
2.
3.
P3
4.
P2
D
Shortage
QS
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Q
3
Chapter 2
Price is below
the market
clearing price
– P2
Q D > QS
Price rises to
the marketclearing price
Market adjusts
to equilibrium
QD
Quantity
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The Market Mechanism
Supply and demand interact to determine
the market-clearing price.
When not in equilibrium, the market will
adjust to alleviate a shortage or surplus
and return the market to equilibrium.
Markets must be competitive for the
mechanism to be efficient.
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Changes In Market Equilibrium
Equilibrium prices are determined by the
relative level of supply and demand.
Changes in supply and/or demand will
change in the equilibrium price and/or
quantity in a free market.
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Changes In Market Equilibrium
Raw material prices
fall
P
D
S
S’
S shifts to S’
Surplus at P1
between Q1, Q2
P1
Price adjusts to
equilibrium at P3, Q3 P3
Q1 Q3Q2
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Changes In Market Equilibrium
P
Income Increases
D
D’
S
Demand increases to
D1
Shortage at P1 of Q1, P3
Q2
P1
Equilibrium at P3, Q3
Q1 Q3 Q
Q
2
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Changes In Market Equilibrium
Income Increases &
raw material prices
fall
Quantity increases
If the increase in D is
greater than the
increase in S price
also increases
P
D
D’
S S’
P2
P1
Q1
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Q
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Shifts in Supply and Demand
When supply and demand change
simultaneously, the impact on the
equilibrium price and quantity is
determined by:
1. The relative size and direction of the
change
2. The shape of the supply and demand
models
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The Price of a College Education
The real price of a college education rose
55 percent from 1970 to 2002.
Increases in costs of modern classrooms
and wages increased costs of production
– decrease in supply
Due to a larger percentage of high school
graduates attending college, demand
increased
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Market for a College Education
S2002
P
(annual cost
in 1970
dollars)
$3,917
S1970
New
equilibrium
was reached
at $4,573 and
a quantity of
12.3 million
students
$2,530
D1970
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13.2
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D2002
Q (millions
enrolled))
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The Long-Run Behavior
of Natural Resource Prices
Consumption of copper has increased about
a hundred fold from 1880 through 2002.
The long term real price for copper has
remained relatively constant.
Increased demand as world economy grew
Decreased production costs increased
supply
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Resource Market Equilibrium
Price
S1900
S1950
S2002
Long-Run Path of
Price and Consumption
D1900
D1950
D2002
Quantity
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Resource Market
Conclusion
Decreases in the costs of production have
increased the supply by more than enough to
offset the increase in demand.
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Elasticities of Supply and Demand
Not only are we concerned with what direction
price and quantity will move when the market
changes, but we are concerned about how
much they change.
Elasticity gives a way to measure by how much
a variable will change with the change in
another variable.
Specifically, it gives the percentage change in
one variable resulting from a one percent
change in another.
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Price Elasticity of Demand
Measures the sensitivity of quantity
demanded to price changes.
It measures the percentage change in the
quantity demanded of a good that results
from a one percent change in price.
D
EP
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%Q D
%P
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Price Elasticity of Demand
The percentage change in a variable is
the absolute change in the variable
divided by the original level of the
variable.
Therefore, elasticity can also be written
as:
Q Q P Q
E
P P Q P
D
P
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Price Elasticity of Demand
Usually a negative number
As price increases, quantity decreases
As price decreases, quantity increases
When EP > 1, the good is price elastic
%Q > % P
When EP < 1, the good is price inelastic
%Q < % P
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Price Elasticity of Demand
The primary determinant of price
elasticity of demand is the availability of
substitutes.
Many substitutes demand is price elastic
Can
easily move to another good with price
increases
Few substitutes demand is price inelastic
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Price Elasticity of Demand
Looking at a linear demand curve, as we
move along the curve Q/P will change
Price elasticity of demand must therefore
be measured at a particular point on the
demand curve
Elasticity will change along the demand
curve in a particular way
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Price Elasticity of Demand
Given a linear demand curve
Elasticity depends on slope and on the
values of P and Q
The top portion of demand curve is elastic
Price
is high and quantity small
The bottom portion of demand curve is
inelastic
Price
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is low and quantity high
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Price Elasticity of Demand
Price
4
EP = -
Demand Curve
Q = 8 – 2P
Elastic
Ep = -1
2
Inelastic
4
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Q
Ep = 0
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Price Elasticity of Demand
The steeper the demand curve becomes,
the more inelastic the good.
The flatter the demand curve becomes,
the more elastic the good
Two extreme cases of demand curves
Completely inelastic demand – vertical
Infinitely elastic demand - horizontal
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Infinitely Elastic Demand
Price
EP =
D
P*
Quantity
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Completely Inelastic Demand
Price
D
EP = 0
Q*
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Other Demand Elasticities
Income Elasticity of Demand
Measures how much quantity demanded
changes with a change in income.
Q/Q
I Q
EI
I/I
Q I
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Other Demand Elasticities
Cross-Price Elasticity of Demand
Measures the percentage change in the
quantity demanded of one good that results
from a one percent change in the price of
another good.
EQb Pm
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Qb Qb Pm Qb
Pm Pm Qb Pm
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Other Demand Elasticities
Complements: Cars and Tires
Cross-price elasticity of demand is negative
Price
of cars increases, quantity demanded of
tired decreases
Substitutes: Butter and Margarine
Cross-price elasticity of demand is positive
Price
of butter increases, quantity of margarine
demanded increases
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Price Elasticity of Supply
Measures the sensitivity of quantity
supplied given a change in price
Measures the percentage change in quantity
supplied resulting from a 1 percent change in
price.
S
S
EP
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% ΔQ
% ΔP
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Point v. Arc Elasticities
Point elasticity of demand
Price elasticity of demand at a particular
point on the demand curve
Arc elasticity of demand
Price elasticity of demand calculated over a
range of prices
D
EP
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ΔQ
P
ΔP Q
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Elasticity: An Application
During 1980’s and 1990’s, market for
wheat went through changes that had
great implications for American farmers
and US agricultural policy
Using the supply and demand curves for
wheat, we can analyze what occurred in
this market
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Elasticity: An Application
Supply: QS = 1900 + 240P
Demand: QD = 3550 – 266P
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Elasticity: An Application
QD = QS
1800 + 240P = 3550 – 266P
506P = 1750
P = $3.46 per bushel
Q = 1800 + (240)(3.46) = 2630 million
bushels
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Elasticity: An Application
We can find the elasticities of demand
and supply at these points
P QD
3.46
E
(266) .035
Q P
2,630
D
P
P QS
3.46
E
(240) .032
Q P
2,630
S
P
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Elasticity: An Application
Assume the price of wheat is
$4.00/bushel due to decrease in supply
QD 3,550 (266)(4.00) 2,486
4.00
E
(266) 0.43
2,486
D
P
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Elasticity: An Application
In 2002, the supply and demand for
wheat were:
Supply: QS = 1439 + 267P
Demand: QD = 2809 – 226P
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Elasticity: An Application
QD = QS
2809 - 226P = 1439 + 267P
P = $2.78 per bushel
Q = 2809 - (226)(2.78) = 2181 million
bushels
Price of wheat fell in nominal terms.
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Short-Run Versus Long-Run
Elasticity
Price elasticity varies with the amount of
time consumers have to respond to a
price.
Short run demand and supply curves
often look very different from their longrun counterparts.
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Short-Run Versus Long-Run
Elasticity
Demand
In general, demand is much more price
elastic in the long run
Consumers
take time to adjust consumption
habits
Demand might be linked to another good that
changes slowly
More substitutes are usually available in the
long run
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Gasoline: Short-Run and Long-Run
Demand Curves
Price
DSR
•People cannot easily
adjust consumption in
short run.
•In the long run, people
tend to drive smaller and
more fuel efficient cars.
DLR
Quantity of Gas
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Short-Run Versus Long-Run
Elasticity
Demand and Durability
For some durable goods, demand is more
elastic in the short run
If goods are durable, then when price
increases, consumers choose to hold on to
the good instead of replacing it so its quantity
demanded fall sharply.
But in long run, older durable goods will have
to be replaced
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Cars: Short-Run and Long-Run
Demand Curves
Price
DLR
•Initially, people may put
off immediate car
purchase
•In long run, older cars
must be replaced.
DSR
Quantity of Cars
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Short-Run Versus Long-Run
Elasticity
Income elasticity also varies with the
amount of time consumers have to
respond to an income change.
For most goods and services, income
elasticity is larger in the long run
When income changes, it takes time to
adjust spending
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Short-Run Versus Long-Run
Elasticity
Income elasticity of durable goods
Income elasticity is less in the long-run than
in the short-run.
Increases
in income mean consumers will want
to hold more cars.
Once older cars replaced, purchases will only to
be to replace old cars.
Less purchases from income increase in long
run than in short run
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Demand for Gasoline
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Demand for Automobiles
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Short-Run Versus Long-Run
Elasticity
Most goods and services:
Long-run price elasticity of supply is greater
than short-run price elasticity of supply.
Other Goods (durables, recyclables):
Long-run price elasticity of supply is less
than short-run price elasticity of supply
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Short-Run Versus Long-Run
Elasticity
SSR
Price
SLR
Due to limited
capacity, firms
are limited by
output constraints
in the short-run.
In the long-run, they
can expand.
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Quantity Primary Copper
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Short-Run Versus Long-Run
Elasticity
SLR
Price
SSR
Price increases
provide an incentive
to convert scrap
copper into new supply.
In the long-run, this
stock of scrap copper
begins to fall.
Quantity Secondary Copper
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Supply of Copper
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Short-Run v. Long-Run Elasticity
– An Application
Why are coffee prices very volatile?
Most of the world’s coffee produced in Brazil.
Many changing weather conditions affect the
crop of coffee, thereby affecting price
Price following bad weather conditions is
usually short-lived
In long run, prices come back to original
levels, all else equal
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Price of Brazilian Coffee
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Short-Run v. Long-Run Elasticity
– An Application
Demand and supply are more elastic in
the long run
In short-run, supply is completely
inelastic
Weather may destroy part of the fixed supply,
decreasing supply
Demand relatively inelastic as well
Price increases significantly
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An Application - Coffee
Price
S’
S
A freeze or drought
decreases the supply
of coffee
Price increases
significantly due to
inelastic supply and
demand
P1
P0
D
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Q1
Q0
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An Application - Coffee
Price
S’
S
Intermediate-Run
1) Supply and demand are
more elastic
2) Price falls back to P2.
P2
P0
D
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Q2 Q0
Quantity
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An Application - Coffee
Price
Long-Run
1) Supply is extremely elastic.
2) Price falls back to P0.
3) Quantity back to Q0.
S
P0
D
Q0
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Predicting the Effects of
Changing Market Conditions
Supply and demand analysis can be
used to predict the effects of changing
market conditions
Linear demand and supply must be fit to
market data
Given
equilibrium price and quantity along with
elasticities of supply and demand, we can
calculate the curves that fit the information
We can then calculate changes in the market
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Predicting the Effects of
Changing Market Conditions
We know
Equilibrium Price, P*=$0.75
Equilibrium Quantity, Q*=7.5
Price elasticity of supply, ES=1.6
Price elasticity of demand, ED=-0.8
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Predicting the Effects of
Changing Market Conditions
Let’s begin with the equations for supply,
demand, elasticity:
Demand: Q = a – bP
Supply: Q = c + dP
Elasticity: (P/Q)(Q/P)
We must calculate numbers for a, b, c,
and d.
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Predicting the Effects of
Changing Market Conditions
The slope of the demand curve above
equals Q/P which equals –b
The slope of the supply curve above
equals Q/P which equals d
Demand: ED = -b(P*/Q*)
Supply: ES = d(P*/Q*)
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Predicting the Effects of
Changing Market Conditions
Price
Supply: Q = c + dP
a/b
ED = -bP*/Q*
ES = dP*/Q*
P*
Demand: Q = a - bP
-c/d
Q*
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Predicting the Effects of
Changing Market Conditions
Using P*, Q* and the elasticities, we can
solve for d and c from supply
ES = d(P*/Q*)
1.6 = d(0.75/7.5) = 0.1d
d = 16
Q = c + dP
7.5 = c + (16)(0.75) = c + 12
c = -4.5
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Predicting the Effects of
Changing Market Conditions
Using P*, Q* and the elasticities, we can
solve for a and b from demand
ED = –b(P*/Q*)
-0.8 = -b(0.75/7.5) = –0.1b
b=8
Q = a – bP
7.5 = a – (8)(0.75) = a – 6
a = 13.5
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Predicting the Effects of
Changing Market Conditions
We now have equations for supply and
demand
Supply: Q = –4.5 + 16P
Demand: Q = 13.5 – 8P
Setting them equal will give up
equilibrium price and quantity with which
we began
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Predicting the Effects of
Changing Market Conditions
Price
Supply: QS = -4.5 + 16P
a/b
.75
Demand: QD = 13.5 - 8P
-c/d
7.5
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Mmt/yr
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Predicting the Effects of
Changing Market Conditions
We have written supply and demand so
that they only depend upon price
Demand could also depend upon other
variable such as income
Demand would then be written as:
Q a bP fI
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Predicting the Effects of
Changing Market Conditions
We know the following information
regarding the copper industry:
I = 1.0
P* = 0.75
Q* = 7.5
b = 8
Income elasticity: E I= 1.3
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Predicting the Effects of
Changing Market Conditions
Using the elasticity of income formula, we
can solve for f
EI = (I/Q)(Q/I)
1.3 = (1.0/7.5)(f)
f = 9.75
Substituting back into demand equation
gives a = 3.75
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Effects of Price Controls
Markets are rarely free of government
intervention
Imposed taxes and granted subsidies
Price controls
Price controls usually hold the price
above or below the equilibrium price
Excess demand – shortage
Excess supply - surplus
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Effects of Price Controls
Price
S
•Price is regulated to
be no higher than Pmax,
•Quantity supplied
falls and quantity
demanded increases
•A shortage results
P0
Pmax
Shortage
QS
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QD Quantity
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Effects of Price Controls
Excess demand sometimes takes the
form of queues
Lines at gas stations during 1974 shortage
Sometimes get curtailments and supply
rationing
Natural gas shortage of the mid ’70’s
Producers typically lose, but some
consumers gain. Some consumers lose.
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Price Controls and
Natural Gas Shortages
In 1954, the federal government began
regulating the wellhead price of natural
gas.
In 1962, the ceiling prices that were
imposed became binding and shortages
resulted.
Price controls created an excess demand
of 7 trillion cubic feet.
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