Firms in Competitive Markets

UAPP693
Economics in the Public & Nonprofit Sectors
Steven W. Peuquet, Ph.D.

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These slides are for use only as part of a formal instructional
course and may not be copied, scanned, or duplicated, in
whole or in part for commercial purposes.

Portions are copywrited by Cengage Learning.

All Rights Reserved.

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 What is a Competitive Market?

 Competitive market
 Market with many buyers and sellers
 Trading identical products

 Each buyer and seller is a price taker

 Firms can freely enter or exit the

market

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 What is a Competitive Market?

 The revenue of a competitive firm

 Maximize profit
 Total revenue minus total cost
 Total
revenue = price times quantity
=PˣQ
 Proportional to the amount of output

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 What is a Competitive Market?

 Average revenue
 Total revenue divided by the quantity sold
 Marginal revenue
 Change in total revenue from an additional
unit sold
 For competitive firms
 Average revenue = P
 Marginal revenue = P

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 Total, Average, and Marginal
Revenue for a Competitive Firm

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 Profit Maximization
 Maximize profit
 Produce quantity where total revenue
minus total cost is greatest
 Compare marginal revenue with marginal
cost
 If MR > MC – increase production
 If MR < MC – decrease production

 Maximize profit where MR = MC

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Table 2
Profit Maximization: A Numerical Example

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 Profit Maximization

 Themarginal-cost curve and the firm’s

supply decision
 MC curve – upward sloping
 ATC curve – U-shaped

 MC curve crosses the ATC curve at the

minimum of ATC curve
 P = AR = MR

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 Profit Maximization

 Rules for profit maximization:

 If MR > MC – firm should increase output
 If MC > MR – firm should decrease output

 If MR = MC – profit-maximizing level of
output
 Marginal-cost curve
 Determines the quantity of the good the
firm is willing to supply at any price
 Is the supply curve

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 Profit Maximization for a Competitive Firm
Costs
The firm maximizes profit by producing
and the quantity at which marginal cost
Revenue equals marginal revenue.
MC

MC2 ATC
P=AR=MR
P=MR1=MR2
AVC

MC1

0 Q1 QMAX Q2 Quantity
This figure shows the marginal-cost curve (MC), the average-total-cost curve (ATC), and the
average-variable-cost curve (AVC). It also shows the market price (P), which equals marginal
revenue (MR) and average revenue (AR). At the quantity Q1, marginal revenue MR1 exceeds
marginal cost MC1, so raising production increases profit. At the quantity Q2, marginal cost MC2
is above marginal revenue MR2, so reducing production increases profit. The profit-maximizing
quantity QMAX is found where the horizontal price line intersects the marginal-cost curve.
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 Marginal Cost as the Competitive Firm’s Supply Curve

Price
MC

P2
ATC

P1 AVC

0 Q1 Q2 Quantity

An increase in the price from P1 to P2 leads to an increase in the firm’s profit-

maximizing quantity from Q1 to Q2. Because the marginal-cost curve shows the
quantity supplied by the firm at any given price, it is the firm’s supply curve.

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 Profit Maximization

 Shutdown
 Short-run decision not to produce anything
 During a specific period of time
 Because of current market conditions

 Firm still has to pay fixed costs

 Exit
 Long-run decision to leave the market
 Firm doesn’t have to pay any costs

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 Profit Maximization
 The
firm’s short-run decision to shut
down
 TR = total revenue
 VC = variable costs

 Firm’s decision:
 Shut down if TR<VC (P<AVC)
 Competitive firm’s short-run supply
curve
 The portion of its marginal-cost curve
 That lies above average variable cost
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 The Competitive Firm’s Short-Run Supply Curve

Costs 1. In the short run, the

firm produces on the MC MC
curve if P>AVC,...

ATC

AVC
2. ...but
shuts down
if P<AVC.

0 Quantity

In the short run, the competitive firm’s supply curve is its marginal-cost curve
(MC) above average variable cost (AVC). If the price falls below average
variable cost, the firm is better off shutting down.
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 Profit Maximization

 Sunk cost
 Has already been committed
 Cannot be recovered

 Ignore them when making decisions

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 Near-empty restaurants
& off-season miniature golf

 Restaurant – stay open for lunch?

 Fixed costs
 Not relevant
 Are sunk costs in short run

 Variablecosts – relevant
 Shut down if revenue from lunch < variable
costs
 Stay open if revenue from lunch > variable
costs

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 Near-empty restaurants
& off-season miniature golf

 Operator of a miniature-golf course

 Ignorefixed costs
 Shut down if
 Revenue < variable costs
 Stay open if
 Revenue > variable costs

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 Profit Maximization
 Firm’s long-run decision
 Exit the market if
 Total revenue < total costs; TR < TC
 Same as: P < ATC
 Enter the market if
 Total revenue > total costs; TR > TC
 Same as: P > ATC

 Competitive firm’s long-run supply curve

 The portion of its marginal-cost curve that
lies above average total cost

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 The Competitive Firm’s Long-Run Supply Curve

Costs 1. In the long run, the firm

produces on the MC curve MC
if P>ATC,...
ATC

2. ...but
exits if
P<ATC

0 Quantity

In the long run, the competitive firm’s supply curve is its marginal-cost
curve (MC) above average total cost (ATC). If the price falls below average
total cost, the firm is better off exiting the market.
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 Profit Maximization

 Measuring profit
 If P > ATC
 Profit = TR – TC = (P – ATC) ˣ Q
 If P < ATC
 Loss = TC - TR = (ATC – P) ˣ Q
 = Negative profit

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 Profit as the Area between Price & Average Total Cost
(a) A firm with profits (b) A firm with losses
Price Price
MC
MC

Profit ATC ATC

Loss
P
ATC P=AR=MR ATC
P
P=AR=MR

0 Q Quantity 0 Q Quantity
(profit-maximizing quantity) (loss-minimizing quantity)

The area of the shaded box between price and average total cost represents the firm’s
profit. The height of this box is price minus average total cost (P – ATC), and the width of
the box is the quantity of output (Q). In panel (a), price is above average total cost, so
the firm has positive profit. In panel (b), price is less than average total cost, so the firm
has losses.
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 Supply Curve

 Short
run: market supply with a fixed
number of firms
 Shortrun – number of firms is fixed
 Each firm supplies quantity where P = MC
 For P > AVC: supply curve is MC curve
 Market supply
 Add up quantity supplied by each firm

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 Short-Run Market Supply
(a) Individual firm supply (b) Market supply
Price Price
MC Supply

$2.00 $2.00

1.00 1.00

0 100 200 Quantity 0 100,000 200,000 Quantity

(firm) (market)

In the short run, the number of firms in the market is fixed. As a result, the market
supply curve, shown in panel (b), reflects the individual firms’ marginal-cost curves,
shown in panel (a). Here, in a market of 1,000 firms, the quantity of output supplied to
the market is 1,000 times the quantity supplied by each firm.
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 Supply Curve

 Long run
 Firms can enter and exit the market
 If P > ATC – firms make positive profit
 New firms enter the market
 If P < ATC – firms make negative profit
 Firms exit the market

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 Supply Curve

 Long run
 Process of entry and exit ends when
 Firms still in market make zero economic
profit (P = ATC)
 Because MC = ATC: Efficient scale

 Long run supply curve – perfectly elastic

 Horizontal at minimum ATC

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 Long-Run Market Supply
(a) Firm’s Zero-Profit Condition (b) Market supply
Price Price

MC
ATC

P=
minimum Supply
ATC

0 Quantity 0 Quantity
(firm) (market)

In the long run, firms will enter or exit the market until profit is driven to zero. As a
result, price equals the minimum of average total cost, as shown in panel (a). The
number of firms adjusts to ensure that all demand is satisfied at this price. The long-
run market supply curve is horizontal at this price, as shown in panel (b).
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 Supply Curve

 Why do competitive firms stay in

business if they make zero profit?
 Profit= total revenue – total cost
 Total cost – includes all opportunity costs

 Zero-profit equilibrium
 Economic profit is zero
 Accounting profit is positive

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 Supply Curve

 Market – in long run equilibrium

P = minimum ATC
 Zero economic profit

 Increase in demand
 Demand curve – shifts outward
 Short run
 Higher quantity
 Higher price: P > ATC – positive economic

profit

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 Supply Curve

 Positive economic profit in short run

 Long run – firms enter the market
 Short run supply curve – shifts right

 Price – decreases back to minimum ATC

 Quantity – increases
 Because there are more firms in the market
 Efficient scale

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 Increase in Demand in the Short Run & Long Run (a)
(a) Initial Condition
Market Firm
Price Price
1. A market begins in 2. …with the firm
long-run equilibrium… earning zero profit.
Short-run supply, S1 MC
ATC

A Long-run
P1 P1
supply

Demand, D1

0 Q1 Quantity 0 Quantity
(market) (firm)

The market starts in a long-run equilibrium, shown as point A in panel (a). In

this equilibrium, each firm makes zero profit, and the price equals the
minimum average total cost.
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 Increase in Demand in the Short Run & Long Run (b)
(b) Short-Run Response
Market Firm
Price Price
3. But then an increase in
4. …leading to
demand raises the price…
short-run profits.
S1 MC
ATC
B
P2 P2
A Long-run
P1 P1
supply

D2
D1

0 Q1 Q 2 Quantity 0 Quantity
(market) (firm)

Panel (b) shows what happens in the short run when demand rises from D1 to D2. The
equilibrium goes from point A to point B, price rises from P1 to P2, and the quantity sold
in the market rises from Q1 to Q2. Because price now exceeds average total cost, firms
make profits, which over time encourage new firms to enter the market.
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 Increase in Demand in the Short Run & Long Run (c)
(c) Long-Run Response
Market Firm
Price Price 6. …restoring long-run
5. When profits induce entry, supply
increases and the price falls,… equilibrium.

S1 MC
S2 ATC
B
P2
A C Long-run
P1 P1
supply

D2
D1

0 Q 1 Q 2 Q3 Quantity 0 Quantity
(market) (firm)

This entry shifts the short-run supply curve to the right from S1 to S2, as shown in panel
(c). In the new long-run equilibrium, point C, price has returned to P1 but the quantity sold
has increased to Q3. Profits are again zero, price is back to the minimum of average total
cost, but the market has more firms to satisfy the greater demand.
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 Supply Curve
 Long-run supply curve might slope
upward
 Some resource used in production may be
available only in limited quantities
 Increase in quantity supplied – increase in costs –
increase in price
 Firms may have different costs
 Some firms earn profit even in the long run
 Long-run supply curve
 More elastic than short-run supply curve
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