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14
Firms in Competitive Markets
PRINCIPLES OF
ECONOMICS
FOURTH EDITION
N. G R E G O R Y M A N K I W
PowerPoint® Slides
by Ron Cronovich
© 2007 Thomson South-Western, all rights reserved
In this chapter, look for the answers to
these questions:
 What is a perfectly competitive market?
 What is marginal revenue? How is it related to
total and average revenue?
 How does a competitive firm determine the
quantity that maximizes profits?
 When might a competitive firm shut down in the
short run? Exit the market in the long run?
 What does the market supply curve look like in the
short run? In the long run?
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FIRMS IN COMPETITIVE MARKETS
1
Introduction: A Scenario
 Three years after graduating, you run your own
business.
 You have to decide how much to produce, what
price to charge, how many workers to hire, etc.
 What factors should affect these decisions?
• Your costs (studied in preceding chapter)
• How much competition you face
 We begin by studying the behavior of firms in
perfectly competitive markets.
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2
Perfect Competition Firm
 In perfect competition all firms are too small to
have any market power and so they will act as
"price-takers" and simply charge the market
price.
 For an industry to be perfectly competitive, there
must be freedom of entry and exit, (No barriers)
all firms must be price-takers, there must be
perfect information, perfect mobility of factors
and the products must be homogenous. (The
same)
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3
Perfectly Competitive Markets
 A market made up of a large number of firms
producing identical products with total freedom
of entry to and exit from the market e.g. wheat.
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4
Characteristics of Perfect Competition
1. Many buyers and many sellers
2. The goods offered for sale are largely the same.
3. Firms can freely enter or exit the market.
 Because of 1 & 2, each buyer and seller is a
“price taker” – takes the price as given.
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The Revenue of a Competitive Firm
 Total revenue (TR)
TR = P x Q
 Average revenue (AR)
TR
=P
AR =
Q
 Marginal Revenue (MR):
The change in TR from
selling one more unit.
CHAPTER 14
∆TR
MR =
∆Q
FIRMS IN COMPETITIVE MARKETS
6
ACTIVE LEARNING
Exercise
1:
Fill in the empty spaces of the table.
Q
P
TR
0
$10
n.a.
1
$10
$10
2
$10
3
$10
4
$10
AR
MR
$40
$10
5
$10
$50
7
ACTIVE LEARNING
Answers
1:
Fill in the empty spaces of the table.
Q
P
TR = P x Q
0
$10
$0
AR =
TR
Q
MR =
∆TR
∆Q
n.a.
$10
1
2
3
$10
$10
$10
Notice that
$20
$10
MR = P
$10
$30
$10
$10
$10
$10
$10
4
$10
$40
$10
$10
5
$10
$50
$10
8
MR = P for a Competitive Firm
 A competitive firm can keep increasing its output
without affecting the market price.
 So, each one-unit increase in Q causes revenue
to rise by P, i.e., MR = P.
MR = P is only true for
firms in competitive markets.
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Profit Maximization
 What Q maximizes the firm’s profit?
 To find the answer,
“Think at the margin.”
If increase Q by one unit,
revenue rises by MR,
cost rises by MC.
 If MR > MC, then increase Q to raise profit.
 If MR < MC, then reduce Q to raise profit.
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10
Profit Maximization
(continued from earlier exercise)
At any Q with
MR > MC,
increasing Q
raises profit.
At any Q with
MR < MC,
reducing Q
raises profit.
CHAPTER 14
Q
TR
TC
0
$0
$5
–$5
1
10
9
1
2
20
15
5
3
30
23
7
4
40
33
7
5
50
45
Profit MR MC
Profit =
MR – MC
$10 $4
$6
10
6
4
10
8
2
10
10
0
10
12
–2
5
FIRMS IN COMPETITIVE MARKETS
11
MC and the Firm’s Supply Decision
Rule: MR = MC at the profit-maximizing Q.
At Qa, MC < MR.
So, increase Q
to raise profit.
Costs
MC
At Qb, MC > MR.
So, reduce Q
to raise profit.
At Q1, MC = MR.
Changing Q
would lower profit.
CHAPTER 14
MR
P1
Q a Q1 Q b
FIRMS IN COMPETITIVE MARKETS
Q
12
MC and the Firm’s Supply Decision
If price rises to P2,
then the profitmaximizing quantity
rises to Q2.
The MC curve
determines the
firm’s Q at any price.
Costs
MC
P2
MR2
P1
MR
Hence,
the MC curve is the
firm’s supply curve.
Q1
CHAPTER 14
FIRMS IN COMPETITIVE MARKETS
Q2
Q
13
Moses Said
 Profit maximization occurs at the quantity where
marginal revenue equals marginal cost.




The Golden Rule!!!
When MR > MC , thou shalt increase Q
When MR < MC , thou shalt decrease Q
thus MR = MC , Profit is maximized.
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Shutdown vs. Exit
 Shutdown:
A short-run decision not to produce anything
because of market conditions.
 Exit:
A long-run decision to leave the market.
 A firm that shuts down temporarily must still pay
its fixed costs. A firm that exits the market does
not have to pay any costs at all, fixed or variable.
CHAPTER 14
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A Firm’s Short-run Decision to Shut Down
 If firm shuts down temporarily,
• revenue falls by TR
• costs fall by VC
 So, the firm should shut down if TR < VC.
 Divide both sides by Q: TR/Q < VC/Q
 So we can write the firm’s decision as:
Shut down if P < AVC
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A Competitive Firm’s SR Supply Curve
The firm’s SR
Costs
supply curve is
the portion of
its MC curve
If P > AVC, then
above
AVC.
firm produces Q
where P = MC.
If P < AVC, then
firm shuts down
(produces Q = 0).
CHAPTER 14
FIRMS IN COMPETITIVE MARKETS
MC
ATC
AVC
Q
17
Short Run Rules
 If Price > ATC, Stay Open with an Economic
Profit.
(P> ATC)
 If Price = ATC, Stay Open with a Normal Profit.
(P=ATC)
 If AVC < price < ATC, Stay Open with a loss.
 If Price <AVC, Shut down.
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The Irrelevance of Sunk Costs
 Sunk cost: a cost that has already been
committed and cannot be recovered
 Sunk costs should be irrelevant to decisions;
you must pay them regardless of your choice.
 FC is a sunk cost: The firm must pay its fixed
costs whether it produces or shuts down.
 So, FC should not matter in the decision to shut
down.
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A Firm’s Long-Run Decision to Exit
 If firm exits the market,
• revenue falls by TR
• costs fall by TC
 So, the firm should exit if TR < TC.
 Divide both sides by Q to rewrite the firm’s
decision as:
Exit if P < ATC
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A New Firm’s Decision to Enter Market
 In the long run, a new firm will enter the market if
it is profitable to do so: if TR > TC.
 Divide both sides by Q to express the firm’s
entry decision as:
Enter if P > ATC
 If P = ATC, Firms will remain in business with a
Normal Profit (P = ATC)
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Long Run Rules
 If Price > ATC, Firms Enter
 If Price = ATC, Nothing happens (Stay)
 If Price < ATC, Firms Exit
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The Competitive Firm’s Supply Curve
The firm’s
LR supply curve
is the portion of
its MC curve
above LRATC.
Costs
MC
LRATC
Q
CHAPTER 14
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25
2A:
Identifying a firm’s profit
ACTIVE LEARNING
A competitive firm
Determine
this firm’s
total profit.
Identify the
area on the
graph that
represents
the firm’s
profit.
Costs, P
MC
MR
ATC
P = $10
$6
50
Q
26
ACTIVE LEARNING
Answers
2A:
A competitive firm
Costs, P
profit per unit
= P – ATC
= $10 – 6
= $4
MC
MR
ATC
P = $10
profit
$6
Total profit
= (P – ATC) x Q
= $4 x 50
= $200
50
Q
27
2B:
Identifying a firm’s loss
ACTIVE LEARNING
A competitive firm
Determine
this firm’s
total loss.
Identify the
area on the
graph that
represents
the firm’s
loss.
Costs, P
MC
ATC
$5
MR
P = $3
30
Q
28
ACTIVE LEARNING
Answers
2B:
A competitive firm
Costs, P
MC
Total loss
= (ATC – P) x Q
= $2 x 30
= $60
ATC
$5
P = $3
loss
loss per unit = $2
MR
30
Q
29
Perfect Competition Long-Run Firm
(P=ATC) (MC=MR) (MC=ATC)
CHAPTER 14
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30
Firm with Ecn Profit, Adjust to Long-Run
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31
Firm with Loss, Adjust to Long-Run
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32
Market Supply: Assumptions
1) All existing firms and potential entrants have
identical costs.
2) Each firm’s costs do not change as other firms
enter or exit the market.
3) The number of firms in the market is
•
•
fixed in the short run
(due to fixed costs)
variable in the long run
(due to free entry and exit)
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33
The SR Market Supply Curve
 As long as P ≥ AVC, each firm will produce its
profit-maximizing quantity, where MR = MC.
 Recall from Chapter 4:
At each price, the market quantity supplied is the
sum of quantity supplied by each firm.
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34
The SR Market Supply Curve
Example: 1000 identical firms.
At each P, market Qs = 1000 x (one firm’s Qs)
P
One firm
MC
P
P3
P3
P2
P2
AVC
P1
Market
S
P1
10 20 30
Q
(firm)
Q
(market)
10,000
CHAPTER 14
FIRMS IN COMPETITIVE MARKETS
20,000 30,000
35
Entry & Exit in the Long Run
 In the LR, the number of firms can change due
to entry & exit.
 If existing firms earn positive economic profit,
• New firms enter.
• SR market supply curve shifts right.
• P falls, reducing firms’ profits.
• Entry stops when firms’ economic profits have
been driven to zero. (MC = ATC)
• All firms remaining are earning a normal
Profit. (P=ATC)
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Entry & Exit in the Long Run
 In the LR, the number of firms can change due
to entry & exit.
 If existing firms incur losses,
• Some will exit the market.
• SR market supply curve shifts left.
• P rises, reducing remaining firms’ losses.
• Exit stops when firms’ economic losses have
been driven to zero. (MC = ATC)
• All firms remaining are earning a normal
Profit. (P=ATC)
CHAPTER 14
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The Zero-Profit Condition
 Long-run equilibrium:
The process of entry or exit is complete –
remaining firms earn zero economic profit.
 Zero economic profit occurs when P = ATC.
 Since firms produce where P = MR = MC,
the zero-profit condition is P = MC = ATC.
 Recall that MC intersects ATC at minimum ATC.
 Hence, in the long run, P = minimum ATC.
 P= ATC, Normal Profit
CHAPTER 14
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38
The LR Market Supply Curve
The LR market supply
curve is horizontal at
P = minimum ATC.
In the long run,
the typical firm
earns zero profit.
P
One firm
MC
P
Market
LRATC
P=
min.
ATC
long-run
supply
Q
(firm)
CHAPTER 14
FIRMS IN COMPETITIVE MARKETS
Q
(market)
39
Why Do Firms Stay in Business if Profit = 0?
 Recall, economic profit is revenue minus all
costs – including implicit costs, like the
opportunity cost of the owner’s time and money.
 In the zero-profit equilibrium, firms earn enough
revenue to cover these costs. Or a Normal
Profit (P=ATC)
CHAPTER 14
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40
SR & LR Effects of an Increase in Demand
…but then an increase
A firm begins in
profits
to zero
…leadingeq’m…
to…driving
SR
Over time,
profits
induce
entry,
in
demand
raises
P,…
long-run
andfirm.
restoring
long-run
eq’m.
profits for the
shifting
S to the
right, reducing P…
P
One firm
Market
P
S1
MC
Profit
ATC
P2
P2
P1
P1
Q
(firm)
CHAPTER 14
S2
B
A
C
long-run
supply
D1
Q1 Q2
FIRMS IN COMPETITIVE MARKETS
Q3
D2
Q
(market)
41
Why the LR Supply Curve Might Slope Upward
 The LR market supply curve is horizontal if
1) all firms have identical costs, and
2) costs do not change as other firms enter or
exit the market.
 If either of these assumptions is not true,
then LR supply curve slopes upward.
CHAPTER 14
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42
1) Firms Have Different Costs
 As P rises, firms with lower costs enter the market
before those with higher costs.
 Further increases in P make it worthwhile
for higher-cost firms to enter the market,
which increases market quantity supplied.
 Hence, LR market supply curve slopes upward.
 At any P,
•
For the marginal firm,
P = minimum ATC and profit = 0.
•
For lower-cost firms, profit > 0.
CHAPTER 14
FIRMS IN COMPETITIVE MARKETS
43
2) Costs Rise as Firms Enter the Market
 In some industries, the supply of a key input is
limited (e.g., there’s a fixed amount of land
suitable for farming).
 The entry of new firms increases demand for this
input, causing its price to rise.
 This increases all firms’ costs.
 Hence, an increase in P is required to increase
the market quantity supplied, so the supply curve
is upward-sloping.
CHAPTER 14
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44
Inputs or Factor Costs
 Up to now we have assumed that input prices
remain constant. Costs rise and fall strictly
because of changes in productivity not because
of changes in factor costs themselves (wages
per hour stay constant for labor).
 A rise in the price of any of the inputs will lead to
the whole set of curves shifting upward.
• If it is a rise in the cost of Capital, then AFC &
ATC will shift up.
• If it is a rise in wages, then AVC, ATC and MC
will shift up.
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FIRMS IN COMPETITIVE MARKETS
45
Inputs or Factor Costs
 A fall in the price of inputs leads to a fall in the
curves.
 If there is an increase in the amount of Capital,
then productivity will rise and the AVC, ATC and
MC curves will all shift down.
• New Technology
• More training
CHAPTER 14
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46
Inputs or Factor Costs
 Determinates of Supply that shift the
cost curves
• Input prices (wages)
• Productivity (Technology)
• Tax & subsidies
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47
lump-sum
 A lump-sum tax is a tax that is a fixed amount,
no matter the change in circumstance of the
taxed entity.
 It is a regressive tax, such that the lower the
income is, the higher the percentage of income
applicable to the tax. An example is a poll tax to
vote, which is unchanged no matter what the
income of the voter.
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48
Lump Sum Tax / Subsidy
 Increase Lump sum tax ~ AFC, ATC shift up
 Decrease in Lump sum tax ~ AFC, ATC shift
down
 Increase Lump sum subsidy ~ AFC, ATC shift
down
 Decrease in Lump sum subsidy ~ AFC, ATC
shift up
 Lump sum tax / subsidy do NOT change AVC,
MC
CHAPTER 14
FIRMS IN COMPETITIVE MARKETS
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Lump Sum Tax / Subsidy
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FIRMS IN COMPETITIVE MARKETS
50
Per Unit Tax / Subsidy
 Increase Per Unit tax ~ AVC, ATC, MC shift up
 Decrease in Per Unit tax ~ AVC, ATC, MC shift
down
 Increase Per Unit subsidy ~ AVC, ATC, MC shift
down
 Decrease in Per Unit subsidy ~ AVC, ATC, MC
shift up
CHAPTER 14
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51
Per Unit Tax / Subsidy
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FIRMS IN COMPETITIVE MARKETS
52
CONCLUSION: The Efficiency of a
Competitive Market
 Profit-maximization:
 Perfect competition:
 So, in the competitive eq’m:
MC = MR
P = MR
P = MC
 Recall, MC is cost of producing the marginal unit.
P is value to buyers of the marginal unit.
 So, the competitive eq’m is efficient, maximizes
total surplus.
 In the next chapter, monopoly: pricing &
production decisions, deadweight loss, regulation.
CHAPTER 14
FIRMS IN COMPETITIVE MARKETS
53
Allocative efficiency
Allocative efficiency refers to the efficiency with
which markets are allocating resources. A market
will be allocatively efficient if it is producing the
right goods for the right people at the right price.
An allocatively efficient market is therefore one
which has no imperfections. This will be true when
marginal cost is equal to average revenue in the
market. It occurs where a firm produces at:
MC = AR (marginal cost pricing).
MC = Price
54
Productive efficiency
A firm is said to be productively efficient when it is
producing at the lowest point on the average cost
curve (MC = ATC).
Productive efficiency is closely related to the
concept of Technical Efficiency. A firm is
technically efficient when it combines the optimal
combination of labor and capital to produce a good.
i.e. cannot produce more of a good, without more
inputs.
55
Allocative & Productive efficiency
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FIRMS IN COMPETITIVE MARKETS
56
CHAPTER SUMMARY
 For a firm in a perfectly competitive market,
price = marginal revenue = average revenue.
 If P > AVC, a firm maximizes profit by producing
the quantity where MR = MC. If P < AVC, a firm
will shut down in the short run.
 If P < ATC, a firm will exit in the long run.
 In the short run, entry is not possible, and an
increase in demand increases firms’ profits.
 With free entry and exit, profits = 0 in the long run,
and P = minimum ATC.
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FIRMS IN COMPETITIVE MARKETS
57