MFC = MRP is the profit-maximizing hiring condition in factor markets: a firm hires workers up to the point where the marginal factor cost (the wage, in a perfectly competitive labor market) equals the marginal revenue product of labor, the extra revenue the last worker generates.
MFC = MRP is the hiring rule that tells a firm exactly how many workers to employ. Marginal factor cost (MFC) is what one more worker costs the firm. Marginal revenue product (MRP) is what one more worker earns the firm in extra revenue. As long as a worker brings in more than they cost (MRP > MFC), hiring them adds to profit, so the firm keeps hiring. The moment the next worker would cost more than they bring in, the firm stops. The profit-maximizing quantity of labor is where the two are equal.
In a perfectly competitive labor market, this rule gets simpler. The firm is a wage taker, so the market sets the wage and the firm can hire as many workers as it wants at that wage. That means MFC is just the constant market wage, and the labor supply curve the firm faces is a horizontal line at that wage (EK PRD-4.C.1). So in Topic 5.3, MFC = MRP collapses into wage = MRP. One more wrinkle from the CED is worth knowing: a firm can be a perfect competitor in the labor market even while it's a monopoly or other imperfect competitor in its output market. The hiring rule still holds either way.
This is the central equation of Unit 5 (Factor Markets) and the heart of Topic 5.3. It directly supports learning objectives 5.3.A (define the characteristics of perfectly competitive factor markets), 5.3.B (explain profit-maximizing hiring behavior using graphs), and 5.3.C (calculate the profit-maximizing quantity of labor from a graph or table). If you can think of it as the factor-market version of MR = MC, the whole unit clicks. In Units 3 and 4 you asked "how much output should I produce?" In Unit 5 you ask "how many workers should I hire?" Same marginal logic, new market. The exam loves testing whether you can run that marginal analysis with a wage and an MRP table in front of you.
Keep studying AP® Microeconomics Unit 5
Marginal Factor Cost (Unit 5)
MFC is one half of the equation. In a perfectly competitive labor market, MFC equals the market wage and the firm's labor supply curve is perfectly elastic, a flat line at the wage. That's why the hiring rule in Topic 5.3 is often written as wage = MRP.
Demand for Labor (Unit 5)
The MRP curve IS the firm's labor demand curve. At every possible wage, MFC = MRP tells the firm how many workers to hire, and tracing those points out gives you the downward-sloping demand for labor. Demand for labor is derived demand, meaning it comes from the demand for the product workers make.
MR = MC Profit Maximization (Units 3-4)
MFC = MRP is the same idea wearing a different outfit. MR = MC finds the profit-maximizing quantity of output; MFC = MRP finds the profit-maximizing quantity of an input. Both say the same thing, which is to keep going until marginal benefit equals marginal cost.
Monopsony (Unit 5)
The rule MFC = MRP still applies when the labor market isn't competitive, but MFC no longer equals the wage. A monopsonist's MFC curve sits above the labor supply curve, so it hires where MFC = MRP but pays a wage below MRP, read off the supply curve. Knowing the competitive case first makes the monopsony graph make sense.
Expect multiple-choice questions that hand you a table of workers, output, and product price and ask for the profit-maximizing number of workers at a given wage. Hire every worker whose MRP is at least the wage, and stop before MRP drops below it (that's EK PRD-4.C.2 in action). Other common stems ask how MFC relates to the labor supply curve in a perfectly competitive labor market (they're the same horizontal line at the market wage) or why a firm stops hiring exactly where MFC = MRP. On FRQs, the Unit 5 graph is a classic: draw a side-by-side of the labor market (market supply and demand setting the wage) and the individual firm (horizontal MFC = wage line crossing the downward-sloping MRP curve), then label the quantity of labor hired. Calculation questions under 5.3.C may also ask you to compute MRP itself, which is marginal product times marginal revenue (or price, for a perfectly competitive seller).
MR = MC answers "how much output should I produce?" while MFC = MRP answers "how many workers should I hire?" They're the same marginal logic applied to different markets. MR = MC lives in the output market (Units 3-4); MFC = MRP lives in the factor market (Unit 5). On the exam, check whether the question is about quantity of a good or quantity of labor before you pick your rule.
A firm maximizes profit by hiring workers until marginal factor cost equals marginal revenue product, because every worker hired before that point adds more to revenue than to cost.
In a perfectly competitive labor market, the firm is a wage taker, so MFC equals the market wage and the firm's labor supply curve is horizontal at that wage.
The MRP curve is the firm's labor demand curve, and MRP equals marginal product of labor times the price (or marginal revenue) of the output.
A firm keeps hiring as long as MRP is greater than the wage and stops before hiring any worker whose MRP falls below the wage.
A firm can be a perfect competitor in the labor market even if it is an imperfect competitor (like a monopoly) in its output market, and MFC = MRP still applies.
MFC = MRP is the factor-market version of MR = MC, so use MFC = MRP whenever the question asks about quantity of labor instead of quantity of output.
It's the profit-maximizing hiring rule from Unit 5, Topic 5.3. A firm hires labor up to the point where the cost of one more worker (MFC) equals the extra revenue that worker generates (MRP).
Only in a perfectly competitive labor market. There, the firm is a wage taker, so MFC is constant at the market wage. Under monopsony, MFC is greater than the wage because hiring an extra worker raises the wage paid to everyone.
MR = MC finds the profit-maximizing quantity of output in Units 3-4; MFC = MRP finds the profit-maximizing quantity of an input like labor in Unit 5. Both rules say to keep going until marginal benefit equals marginal cost, just in different markets.
Compute each worker's MRP (marginal product times product price for a price-taking seller), then hire every worker whose MRP is greater than or equal to the wage. If the wage is $60 and the 4th worker's MRP is $80 but the 5th worker's is $50, you hire 4 workers.
No. The CED (EK PRD-4.C.1) says a firm can be a perfect competitor in the labor market even if it's an imperfect competitor in its output market. The rule still holds; the only difference is you'd compute MRP using marginal revenue instead of price.
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