CA Foundation · Paper 4 · Business Economics

Price-Output Determination under Different Market Forms

Unit 3 · Short Revision Sheet for May 2026 onwards

MCQ Priority Short Notes Quick Revision

Crux First

Most important recall points

Perfect competition → firm is price taker.
Perfect competition → AR = MR = Price.
Firm equilibrium → MR = MC and MC must cut MR from below.
Same market price can exist with different firm outputs.
Short-run supply curve of competitive firm = MC above AVC.
Shutdown rule → Price < AVC.
Long-run perfect competition → only normal profit.
Monopoly → single seller, price maker, AR downward, MR below AR.
Monopoly fixes output first, then takes price from AR curve.
Price discrimination → same product sold in different sub-markets at different prices.
Discriminating monopoly equilibrium → MRA = MRB = MC.
Monopolistic competition → differentiated product, many sellers, long run normal profit + excess capacity.

1. Perfect Competition

Main Features

Large number of buyers and sellers
Homogeneous product
Free entry and exit
Perfect knowledge
Firm is a price taker

Perfect Competition: AR = MR = Price

2. Industry Price and Firm Output

Industry determines market price through total demand and total supply.
Each firm accepts that market price.
But all firms need not sell the same quantity.
At the same market price, one firm may sell 8 units, another 10, another 12 units.

Same market price does not mean same output for every firm.

3. Competitive Firm Equilibrium

Firm is in equilibrium where profit is maximum.
Main condition: MR = MC.
Second condition: MC must cut MR from below.

Since MR = Price, competitive firm chooses output where Price = MC

MCQ Trap

Firm chooses output, not price.
Price is already fixed by the market.

4. Short Run Supply and Shutdown

Competitive firm’s short-run supply curve is the MC curve above AVC.
If price covers AVC, firm continues.
If price falls below AVC, firm shuts down.

Short-run Supply Curve = MC above AVC

Shutdown Rule: Price < AVC

5. Competitive Firm: Profit Situations

Condition	Result
AR > ATC	Supernormal profit
AR = ATC	Normal profit
AVC < AR < ATC	Loss, but continue
AR < AVC	Shutdown

6. Long Run Perfect Competition

Free entry removes supernormal profit.
Free exit removes losses.
In the long run, only normal profit remains.

Long Run: LMC = LAC = P = MR

Long-run perfect competition gives optimum plant use and minimum possible cost.

7. Monopoly

Main Features

Single seller
No close substitute
Strong barriers to entry
Firm is a price maker

In monopoly, firm and industry are the same.

8. Monopoly Revenue and Equilibrium

AR curve slopes downward.
MR curve also slopes downward.
MR lies below AR.
Monopolist chooses output where MR = MC.
After fixing output, price is taken from the AR curve.

Monopoly Equilibrium: MR = MC

Price is read from AR at equilibrium output

MCQ Trap

Monopolist does not choose price first and then output.
It chooses output first, then corresponding price.

9. Monopoly: Short Run and Long Run

In short run, monopoly may earn supernormal profit or suffer loss.
In long run, monopoly can continue to earn supernormal profit because entry is blocked.
Long-run monopoly need not produce at minimum LAC.

10. Price Discrimination

Same product sold at different prices in different markets.
Possible only when seller has control over price.
Market must be separable.
Elasticity of demand should differ across markets.
Resale between markets should not be possible.

Higher price is charged where demand is more inelastic.

11. Two Sub-Markets under Price Discrimination

Monopolist may divide total market into sub-market A and sub-market B.
Total output is first fixed.
Then output is distributed between the two markets.
Different prices may be charged in the two markets.

Equilibrium: MRA = MRB = MC

Total Output: OM = OM1 + OM2

This is the exact “same product, two markets, different prices” logic.

12. Monopolistic Competition

Many sellers and many buyers
Differentiated product
Free entry and exit
Some degree of price control
Demand curve slopes downward

Equilibrium: MR = MC

13. Monopolistic Competition: Short Run and Long Run

In short run, firm may earn profit or incur loss.
In long run, entry and exit reduce everything to normal profit.
But firm does not produce at optimum capacity.

Long Run: Normal Profit + Excess Capacity

14. Quick Comparison

Feature	Perfect Competition	Monopoly	Monopolistic Competition
Sellers	Many	One	Many
Product	Homogeneous	No close substitute	Differentiated
Price Control	None	High	Some
Demand Curve	Horizontal	Downward sloping	Downward sloping
Long-run Profit	Normal only	Can continue supernormal	Normal only

Final Quick Revision

1-minute recall before MCQs

Perfect competition → price taker.
Perfect competition → AR = MR = Price.
Competitive equilibrium → MR = MC.
Same price can exist with different outputs by different firms.
Short-run supply curve = MC above AVC.
Shutdown → Price < AVC.
Long-run perfect competition → only normal profit.
Monopoly → price maker, MR below AR.
Monopoly chooses output first, then price from AR.
Price discrimination → two markets, different prices.
Discriminating monopoly equilibrium → MRA = MRB = MC.
Monopolistic competition → differentiated product.
Long-run monopolistic competition → normal profit + excess capacity.