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AP Microeconomics · Unit 5 of 6
Factor Markets
10–13% of the exam8 lessons · 110 min36 terms
What this unit covers
The topics below follow the published Micro course framework for Unit 5. This unit is worth 10–13% of the exam, so budget your time against that rather than against how long the unit takes to teach.
Derived demandLabor marketsMRPWage determination
Lessons in this unit
- Derived Demand & Marginal Revenue Product14 min · 3 objectivesExplain why the demand for a factor of production is a derived demand · Calculate marginal revenue product and marginal resource cost · Apply the profit-maximizing hiring rule MRP = MRC
- Competitive Labor Markets & Wage Determination14 min · 3 objectivesExplain how equilibrium wages are set in a competitive labor market · Identify the determinants that shift labor demand and labor supply · Relate the firm’s wage-taking behavior to the market wage
- Monopsony & the Least-Cost Rule13 min · 3 objectivesExplain how a monopsony sets wages and employment below competitive levels · Distinguish marginal resource cost from the wage in a monopsony · Apply the least-cost combination rule for hiring multiple inputs
- Derived Demand & What Shifts MRP14 min · 3 objectivesExplain why labor demand is derived from product demand · Compute marginal revenue product from a production schedule · Identify what shifts the MRP curve and predict the effect on wages
- The Least-Cost Rule & Choosing Between Inputs13 min · 3 objectivesApply the least-cost rule to allocate spending between two inputs · Distinguish the least-cost rule from the profit-maximizing rule · Predict input substitution following a change in an input price
- Monopsony: Why Marginal Factor Cost Exceeds the Wage15 min · 3 objectivesExplain why a monopsonist faces a marginal factor cost above the labor supply curve · Compute marginal factor cost from a labor supply schedule · Locate the monopsony wage and employment level on the graph
- The Minimum Wage in Two Market Structures14 min · 3 objectivesPredict the effect of a binding minimum wage in a competitive labor market · Explain why a minimum wage can raise employment under monopsony · Identify what determines the size of the employment effect
- Shifts in Factor Supply & Wage Differentials13 min · 3 objectivesIdentify what shifts the supply of labor to an occupation or region · Explain wage differentials in terms of supply, demand and compensating differentials · Explain how unions and licensing affect the labor market graph
Formulas in Unit 5
Factor hiring
MRP = MP × MR (= MP × P in a competitive product market) · Hire until MRP = MRC
MRP is the extra revenue from one more unit of the factor; MRC is its extra cost. In a competitive labor market MRC equals the market wage.
Competitive labor market equilibrium
Market: labor demand (ΣMRP) = labor supply → sets wage · Firm: hires where MRP = wage (MRC)
The market sets the wage; the wage-taking firm faces a horizontal labor-supply curve at that wage and hires until MRP falls to it.
Least-cost and profit-max input rules
Least-cost: MPL / PL = MPK / PK · Profit-max: MRPL / PL = MRPK / PK = 1
Equalizing marginal product per dollar minimizes cost for a given output; hiring each input until MRP = its price maximizes profit and satisfies the least-cost rule too.
Marginal revenue product
MRP = MP × MR · in a competitive product market MR = P, so MRP = MP × P
Two things can change MRP: the worker's physical productivity (MP) or the price of the output (P). Both shift labor demand.
The two rules
least-cost: MP_L / P_L = MP_K / P_K · profit-maximizing: MRP_L / P_L = MRP_K / P_K = 1
Least cost equalizes output per dollar. Profit maximization additionally requires each ratio to equal one — each input paying for itself exactly.
Marginal factor cost
MFC = Δ(total labor cost) / Δ(workers) · MFC > wage for a monopsonist, MFC = wage in a competitive labor market
The exact structural parallel to marginal revenue for a monopolist: MR < price because of the price cut on all units; MFC > wage because of the raise on all workers.
The two outcomes
competitive market: binding minimum → wage ↑, employment ↓, labor surplus · monopsony (minimum between monopsony and competitive wage): wage ↑, employment ↑
Same policy, opposite employment effect. The market structure is what decides it, which is why questions always specify the structure.
Explaining a wage gap
high wage = high MRP (productivity or output price) and/or restricted supply (skill, licensing, unpleasantness)
Any wage differential is a supply story, a demand story, or both. Naming which is what a free response wants.
Every term in Unit 5
All 36 terms we publish for Factor Markets, with definitions. Reading them through is the fastest way to find the ones you cannot define — then drill those in cram mode until you can produce them without the prompt.
- Derived demand
- Factor demand comes from demand for the output. A collapse in product demand collapses labor demand with nothing changing about the workers.
- Marginal revenue product (MRP)
- The extra revenue from hiring one more unit of a factor: marginal product times marginal revenue. For a firm selling in a competitive product market, MRP = MP × P.
- Why MRP slopes downward
- Diminishing marginal returns lower marginal product as more of the factor is hired — and for a firm with market power, marginal revenue falls too, so MRP falls twice as fast.
- Marginal resource cost (MRC)
- The extra cost of hiring one more unit of a factor. Equal to the wage for a firm hiring in a competitive labor market.
- Profit-maximizing hiring rule
- Hire where MRP = MRC. The factor-market twin of MR = MC, and it determines quantity of labor rather than quantity of output.
- Least-cost combination rule
- MPL / PL = MPK / PK. Allocate spending across inputs so the marginal product per dollar is equal for each.
- Profit-maximizing combination of inputs
- MRPL / PL = MRPK / PK = 1. Stronger than the least-cost rule: it fixes the scale of production as well as the mix.
- Labor supply curve for an individual
- Upward-sloping over the usual range, because a higher wage raises the opportunity cost of leisure. It can bend backward at very high wages when the income effect dominates.
- Perfectly competitive labor market
- Many small employers and workers, identical labor. The market sets the wage; the individual firm faces a horizontal labor supply curve, so wage = MRC.
- Market vs firm graph in factor markets
- The market graph sets the wage from labor supply and demand; the firm takes it as horizontal and hires where MRP meets it. The same two-graph structure as product markets.
- Shifters of labor demand
- Product demand, productivity, and the prices of substitute or complementary inputs. All work through MRP.
- Shifters of labor supply
- Number of qualified workers, wages in alternative occupations, non-wage amenities, immigration, and preferences for leisure.
- Monopsony
- A single buyer of labor. It faces the upward-sloping market labor supply curve, so hiring one more worker raises the wage paid to all workers.
- Why MRC lies above supply for a monopsonist
- Hiring one more worker requires raising the wage for every worker already employed, so the marginal cost of that worker exceeds their wage.
- Monopsony outcome
- Hire where MRP = MRC, then read the wage down on the labor supply curve. Both employment and the wage are below the competitive level.
- Minimum wage under monopsony
- A minimum wage set between the monopsony wage and the competitive wage can raise both the wage and employment — the exception to the usual price-floor result, and a favorite exam question.
- Economic rent
- Payment to a factor above the minimum needed to keep it in its current use. Large when supply is inelastic, which is why land earns rent.
- Wage differentials
- Persistent wage differences from human capital, compensating differentials for unpleasant or risky work, discrimination, and barriers to mobility.
- Compensating differential
- Extra pay to offset undesirable job characteristics — danger, night shifts, isolation. It equalizes the total attractiveness of jobs, not the wage.
- Human capital
- Education, training and experience embodied in workers. It raises marginal product and so raises MRP and the equilibrium wage.
- MRP
- MRP = MP × MR, and MR = P only in a competitive product market. A monopolist's MRP is below MP × P, so it hires fewer workers.
- The hiring rule
- Hire while MRP > wage, stop at MRP = wage. In a competitive labor market the MRP curve IS the firm's labor demand curve.
- What shifts MRP
- Output price, worker productivity, and the quantity of complementary capital. NOT the wage — the wage decides where on the curve you sit.
- Least-cost rule
- MP_L/P_L = MP_K/P_K. Equalize output per DOLLAR, not per unit. A more productive input can still be the worse buy.
- Profit-maximizing input rule
- MRP_L/P_L = MRP_K/P_K = 1. Equal ratios give the cheapest mix; ratios equal to one also pin down the right quantity.
- Input substitution
- When an input gets dearer its output-per-dollar falls and the firm substitutes toward the other. This is why higher wages encourage automation.
- Why MFC exceeds the wage under monopsony
- Hiring one more worker requires a higher wage paid to EVERYONE already employed. MFC is the new wage plus all the raises.
- MFC is the mirror of MR
- MR < price because of the price cut on all units; MFC > wage because of the raise for all workers. Same structure, opposite side of the market.
- The monopsony two-step
- Quantity from MRP = MFC, then the wage from the SUPPLY curve at that quantity. The wage ends below MRP.
- Monopsony versus competition
- Fewer workers at a lower wage. Hiring where MRP = MFC stops earlier than where MRP = wage, since MFC is higher.
- Minimum wage in a competitive market
- A binding minimum creates a labor surplus. Employment falls to quantity demanded at the higher wage.
- The range condition on the monopsony result
- It holds only for a minimum between the monopsony and competitive wage. Above the competitive wage, employment falls as usual.
- What determines the employment loss
- The elasticity of labor demand. Inelastic — few substitutes, labor a small cost share — means a small loss. Elastic means a large one.
- What shifts labor supply to an occupation
- Number of qualified workers, wages elsewhere, non-wage attractiveness, migration, and training or licensing requirements.
- How licensing raises wages
- By shifting supply LEFT — fewer workers meet the requirement. Whether it also raises quality is a separate question.
- Union wage above equilibrium
- Higher pay for those employed, fewer employed overall. Structurally identical to a binding minimum wage in a competitive market.
What examiners penalize here
- The hiring rule **MRP = MRC** is the factor-market twin of the product-market rule MR = MC. In a competitive labor market, set **MRP = wage**. Always confirm whether the *product* market is competitive before using MRP = MP × P.
- Free-response items often pair a **market** labor diagram (setting the wage) with a **firm** diagram (MRP = wage). Show the wage determined in the market, then carry that horizontal wage line to the firm’s MRP curve to find how many workers it hires.
- For least-cost problems, compute **marginal product per dollar** (MP ÷ input price) for each input and shift toward the higher one until they equalize. Do not compare raw marginal products when input prices differ — always divide by price first.
- When a table gives total product, compute marginal product and then MRP as separate columns. Rubrics award the MRP column, and skipping straight to a hiring number forfeits that credit.
- Write both ratios as decimals side by side before concluding anything. The comparison is the whole answer, and rubrics reward showing the two computed values rather than just naming which input to use more of.
- Label four things on a monopsony graph: MRP, supply, MFC, and the chosen quantity. Then mark the wage on supply and MRP directly above it — the vertical gap between them is the monopsonistic exploitation the question will ask you to identify.
- Read the market structure before answering any minimum-wage question. "Perfectly competitive labor market" and "the sole employer in the region" call for opposite employment answers, and the wording is the only signal.
- When explaining a wage differential, give one demand-side and one supply-side reason. Rubrics frequently award one point for each, and answers that offer two versions of the same story earn only one.
Practice Micro
Our practice bank is drawn from across the whole course rather than filtered to one unit, which is closer to how the exam asks anyway — it will not tell you which unit a question is testing.
Questions about this unit
How much of the AP Microeconomics exam is Unit 5?
Unit 5, Factor Markets, is worth 10–13% of the Micro multiple-choice section according to the published course framework. Across all 6 units that makes it a substantial share — heavier than an even split would give it.
What topics are covered in Micro Unit 5?
Factor Markets covers Derived demand, Labor markets, MRP and Wage determination. We publish 36 terms with definitions for this unit, all of them on this page.
How should I study Micro Unit 5?
Read the 8 lessons below first — about 110 minutes — then drill the 36 terms in cram mode until you can produce each definition from memory rather than just recognize it. Recognition is what makes a unit feel finished when it is not. Finish with practice questions and read the explanation for every one you get right by elimination as well as the ones you miss.
All 6 units of AP Microeconomics
Unit names, topics and exam weights follow the published College Board course framework for AP Microeconomics. AP® is a trademark registered by the College Board, which does not endorse this site.