Market Graph vs Firm Graph: Transfer Price, Then Find Output
Read the market graph first, then carry its price to the firm graph. A price-taking firm chooses its own output at that price. Compare two linked graphs, work through market and firm quantities separately, and try three original interactive questions.
A price-taking firm cannot choose the price delivered by the market.
Compare Three Market and Firm Cases
The cases assume a small price-taking firm, unchanged costs unless a cost shock is stated, and profit-maximizing output choices. In the discrete case, the listed increasing marginal costs cover all feasible units from one to five, and fixed cost is unavoidable over the operating period. Compare operating contribution with shutdown; do not assume that a positive output rule alone means positive economic profit.
A competitive firm’s price is $18. Marginal cost for quantities 1 through 5 is $6, $10, $14, $19, and $25. What quantity maximizes profit?
- 3
- 2
- 4
- 5
- 1
3 The firm produces the first three units because their marginal costs do not exceed $18. The fourth unit costs $19 at the margin.
A price-taking bakery receives $1,700 in revenue and incurs $1,400 in variable cost. Its producer surplus is
- $170
- $700
- $300
- $1,400
- $1,700
$300 Producer surplus is revenue minus variable cost: $1,700 – $1,400 = $300. Fixed cost is not subtracted from producer surplus.
A competitive wheat market sets a price of $6 per bushel. What should be carried from the market graph to the graph of one price-taking farm?
- The entire market demand curve
- The market quantity
- A horizontal price line at $6
- The market supply curve
- The number of farms
A horizontal price line at $6 The market intersection determines price. One small farm then treats that price as given, so its demand and marginal-revenue line is horizontal at $6. The farm’s output is found separately where that line meets its marginal cost.
Video Lesson: Competitive Firms and Market Price
A focused video lesson from Jacob Clifford.
Start with the Market Shock
For a demand increase with market supply held fixed, first find the new market price. In the short-run response after variable inputs can adjust, move the representative firm’s horizontal P=MR line upward. Use its unchanged rising MC to find output, then compare revenue with the appropriate costs. The market panel explains the price change; the firm panel explains the firm’s response.
Label Industry Q and Firm q
Use capital Q for industry quantity and lowercase q for one firm’s output. With 200 identical firms producing fifteen units each, Q=3,000 and q=15. Aggregate their outputs for the market total. In this many-firm example, assigning the whole market’s sales to one firm would contradict the stated small-firm setup; the two quantity axes have different meanings.
Follow the Four-Step Graph Sequence
| Step | Market graph | Firm graph |
|---|---|---|
| 1 | Shift demand or supply | Hold curves until price is known |
| 2 | Read new equilibrium price and Q |
Transfer price as horizontal P=MR |
| 3 | – | Find q where price meets rising MC |
| 4 | – | Compare price with AVC and ATC |
Trace a Market-Supply Increase
For a market-supply increase with demand fixed, market price falls and the firm’s horizontal revenue line moves down. With an unchanged rising MC, its best operating output falls. Compare the best operating payoff with shutdown: under the standard cost assumptions it operates when price covers AVC at the chosen output, and shuts down if price is below minimum AVC. Keep market quantity Q separate from firm quantity q.
Read a Separate Demand-Shift Example
As a separate supplied-graph illustration, market demand raises price from $12 to $17. One firm’s MC intersections are forty and fifty-five units respectively, and its ATC at fifty-five is $14. Its profit is (17-14)55=$165. These graph values are not the cost function used in the linked model below. They illustrate the sequence: market price, firm output, then the ATC gap.
Identify the Adjustment Horizon
If the profit is expected to be available to entrants and entry is possible, later entry can change market supply and price again. A short-run question holds seller count fixed while variable inputs can adjust; a long-run question may permit entry or exit. The word “immediately” alone should not be taken as proof that every output adjustment has already occurred.
Separate Individual and Industry Cost Shocks
Under the small-firm assumption, an individual firm’s cost change has negligible effect on market price when other market conditions are held fixed, but it can change that firm’s output. A cost change affecting the industry can alter both individual cost curves and market supply. Identify the scope of the shock before deciding which curves stay fixed.
Move the Revenue Line in the Right Direction
The horizontal revenue line moves vertically when the market price changes; it does not become a downward-sloping market demand curve. A horizontal line’s left or right movement does not represent a new price. On the firm panel, distinguish that revenue-line change from movement along an unchanged MC curve or an actual shift of MC.
Calculate Profit from Supplied Graph Values
In another separate supplied-graph illustration, market price is $18 and one firm’s rising MC reaches $18 at forty units. Its AVC there is $11 and ATC is $15. Assuming this is the best operating output, the firm produces forty and earns (18-15)(40)=$120. Price covering AVC supports operation; total average cost is used for economic profit. This example is separate from the linked model below.
Transfer Price and Complete the Cost Checks
Find market equilibrium price, transfer it as a horizontal price and MR line, then locate the firm’s best operating output and compare shutdown. Check profit using total cost or ATC. Do not carry industry quantity to one firm’s quantity axis; if seller count or cost curves change, update the appropriate panel first.
The linked example below deliberately uses one internally consistent cost function for both demand scenarios. It holds seller count fixed at twenty so you can isolate the short-run price transfer. Later free entry is a different adjustment and requires a different market supply curve.
Read the Price-Taking and Output Explanation
OpenStax’s competitive output lesson connects market price with a firm’s revenue line, output choice and shutdown comparison. The paired graphs, equations and questions below use an independent hypothetical model, not copied textbook figures or exercises.
Try the Linked Market and Firm Graphs
Twenty identical firms each have total economic cost TC = 0.2q² + 180 and MC = 0.4q. The $180 is unavoidable over this operating period. Each firm takes price as given and chooses q = 2.5P when operating, so the twenty firms together supply Q = 50P. Initial demand is Q = 1,200 − 50P; higher demand is Q = 1,800 − 50P.
Compare two short-run demand scenarios with twenty firms and unchanged costs. Choose a demand button; if the controls are unavailable, use the two-row comparison table below.
Original demand: P = $12; market Q = 600; firm q = 30; firm economic profit = $0. Twenty firms remain.
The market panel determines price. Carry that price to the firm’s horizontal P = MR line, then use its unchanged MC curve to find q. The quantity axes have different scales. These controls hold the number of firms at twenty; they do not depict long-run entry.
Check Both Scenarios Numerically
| Demand scenario | Price | Market Q | Firm q | Economic profit per firm |
|---|---|---|---|---|
| Original | $12 | 600 | 30 | $0 |
| Higher, short run | $18 | 900 | 45 | $225 |
Initially set 50P = 1,200 − 50P: P = $12, Q = 600 and q = 30. After the demand shift, 50P = 1,800 − 50P gives P = $18, Q = 900 and q = 45. One firm’s revenue then is $810 and total economic cost is 0.2(45²) + 180 = $585, leaving $225 profit. Carrying market Q = 900 to the firm panel would substitute the industry’s output for one firm’s forty-five units.
Check Operation, Profit and Later Entry
Why does the higher-demand firm operate, and what would later free entry change if costs remain unchanged?
Check your reasoning
At q = 45, variable cost is $405 and revenue is $810, so operating contribution is $405. After the $180 fixed economic cost, profit is $225, which exceeds the −$180 shutdown payoff. At the original q = 30, revenue and total economic cost both equal $360, while AVC is $6 and price is $12.
For any given price in this model, operating profit equals 1.25P² − 180 − 0.2(q − 2.5P)². Thus q = 2.5P globally maximizes operating profit at the two prices. ATC − 12 = 0.2(q − 30)²/q for positive q, so minimum ATC is $12 at q = 30. With free entry and unchanged industry costs, the higher demand could eventually be served at P = $12, Q = 1,200 by forty firms producing thirty each. That endpoint is not one of the graph buttons: those keep twenty firms fixed.
For a separate producer-surplus comparison using the earlier bakery values, $1,700 revenue minus $1,400 variable cost gives $300 producer surplus. If unavoidable fixed economic cost is $500, economic profit is −$200. Operating still beats a −$500 shutdown payoff. Producer surplus and economic profit subtract different costs.
Try Three Market and Firm Questions
Choose one answer, then check your reasoning. These are short learning checks, not an exam score. If the controls are unavailable, the explanations remain readable below each question.
Answer C. Market supply is Q = 50P. Equating it to 1,800 − 50P gives P = $18 and Q = 900. Each firm produces q = 2.5(18) = 45. The panels share price, not the quantity scale.
Answer D. Producer surplus as defined here is 1,700 − 1,400 = $300. Economic profit also subtracts fixed economic cost, giving 300 − 500 = −$200. That loss is smaller than the −$500 loss from shutting down for the period.
Answer A. The first four units cost 6 + 10 + 14 + 19 = $49 in total variable cost. Revenue is $80, so profit is 80 − 49 − 20 = $11. The fifth unit costs $25 but earns only $20, reducing profit; shutdown gives −$20.
Connect Price Taking with Entry and Equilibrium
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