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EC311 · Intermediate Microeconomics

EC311 / TOPIC 23

7.1 Competitive firms and shutdown

When should a loss-making firm keep producing in the short run?

Produce where P=MC if price covers AVC; fixed cost does not alter the short-run shutdown rule.

Follow the cause and effect

  1. Find q where P=MC on the rising portion.

  2. Check P≥min AVC to choose production versus q=0.

  3. Calculate profit as TR−VC−FC and distinguish long-run exit.

The model you are using

KEY MODEL
TC=36+4q+q²
q*=(P−4)/2 for P>4
q*=0 for P≤4

Conditions for this model

No additional startup costs; FC is paid even at q=0, and firm output does not affect price.

The exam trap

P<ATC means a loss, not immediate shutdown when P still exceeds AVC.

Connect the reasoning to the graph

What changes

  • Firm supply is MC above min AVC, and profit is the rectangle (P−ATC)q.

What stays fixed

No additional startup costs; FC is paid even at q=0, and firm output does not affect price.

Keep these conditions throughout the comparison; change only what the case above specifies.

What to inspect

Calculate profit as TR−VC−FC and distinguish long-run exit.

Compare before and after, and locate the conclusion on the graph.

5 MINUTES · TRANSFER THE IDEA

Can you explain it without the lesson?

Draw P between AVC and ATC, showing loss and the avoided variable-cost comparison.

Lesson references

  • Pindyck & Rubinfeld, Microeconomics, 9th Global ed., pp. 299, 312
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