AP Microeconomics exam technique: how to draw and label the market, cost-curve, and market-structure graphs and answer the free-response questions

What the AP Microeconomics exam actually rewards

AP Microeconomics is won and lost on two skills: drawing fully labelled graphs and reasoning in clear cause-and-effect chains. Because no calculator is allowed and the prose can be short, the free-response section is really a test of whether you can produce the right model, label it correctly, and explain what it shows. This guide pulls together the graphing and calculation technique across all six units, each of which has its own dot-point pages with practice questions: the market graphs of demand, supply, and market equilibrium and surplus; the firm models of perfect competition and monopoly; and the factor-market and externality diagrams.

The golden rule of AP graphs: label everything

Every AP graph earns its points from labels, not just shape. On any diagram you draw:

• Label both axes. For a market graph, the vertical axis is Price (P) and the horizontal axis is Quantity (Q). For the PPC, label each axis with one of the two goods. For a factor market, the axes are the wage and the quantity of labor.
• Name every curve. Demand is D, supply is S, marginal revenue MR, marginal cost MC, average total cost ATC, average variable cost AVC, marginal revenue product MRP, marginal factor cost MFC. When a curve shifts, show both positions (D1 and D2, or S1 and S2).
• Mark the quantity and price. Show the profit-maximizing quantity and the price the firm charges, with dashed lines to the axes if helpful.
• Shade the right area. Profit, loss, and deadweight loss are specific rectangles or triangles; shade and label them.

A correctly shaped but unlabelled graph typically earns zero. The grader checks specific labels against a rubric, so labelling is where the marks are.

The supply and demand graph and shifts

The market graph is the workhorse of Unit 2. The make-or-break skill is distinguishing a movement along a curve from a shift of the curve:

For a single shift, redraw the curve, find the new intersection, and read off the new equilibrium. Remember the four single-shift outcomes: a demand increase raises both price and quantity; a demand decrease lowers both; a supply increase lowers price and raises quantity; a supply decrease raises price and lowers quantity. For a double shift, one of price and quantity is determinate and the other indeterminate, identify which both shifts push the same way (determinate) and which they push opposite ways (indeterminate), and say so explicitly.

The firm's cost curves and the market structures

Unit 3 and Unit 4 add the firm's cost curves and the four market structures. Learn these conventions once and they apply everywhere:

• Perfect competition. The firm faces a horizontal demand line at the market price (price = MR), produces where P = MC, and in the long run sits at minimum ATC with zero economic profit. Show profit or loss as the rectangle between price and ATC.
• Monopoly and monopolistic competition. The firm faces a downward-sloping demand curve with MR below it. Use the two-step method: find quantity where MR = MC, then read the price up to the demand curve. Monopolistic competition ends in long-run tangency of demand to ATC (zero profit, excess capacity).
• Deadweight loss. For a monopoly, it is the triangle between demand and MC from the monopoly quantity out to the efficient quantity (where P = MC).

The factor-market and externality graphs

• Competitive factor market. Downward-sloping MRP (factor demand) and upward-sloping factor supply; hire where MRP = wage.
• Monopsony. The MFC curve lies above the upward-sloping supply curve; hire where MRP = MFC, then read the wage down to the supply curve (below MRP). The result is lower wage and employment than competition.
• Externalities. Draw marginal private and marginal social curves. A negative externality puts MSC above MPC (overproduction); a positive externality puts MSB above MPB (underproduction). The deadweight loss is the triangle between the social and private curves over the misallocated quantity; the corrective tax or subsidy equals the marginal external cost or benefit.

The standard calculations

Keep these automatic, and always use the midpoint (average) base for a percentage change:

• Opportunity cost from output data: the other good divided by the good in question.
• Midpoint elasticity $= \dfrac{(Q_2 - Q_1)/((Q_1+Q_2)/2)}{(P_2 - P_1)/((P_1+P_2)/2)}$; take the absolute value for price elasticity of demand, keep the sign for income and cross-price elasticity.
• Total revenue test: elastic, price and revenue move opposite ways; inelastic, same way; unit elastic, revenue unchanged.
• Surplus: consumer surplus is the triangle below demand and above price; producer surplus is above supply and below price; each is $\frac{1}{2} \times \text{base} \times \text{height}$.
• Profit $= (P - ATC) \times Q$, after finding the quantity from MR = MC.
• Marginal revenue product $= MP \times P$ (competitive seller) or $MP \times MR$ (price maker); hire where $MRP = MFC$.

Matching your answer to the task verb

The free-response section uses specific AP task verbs, and each calls for a different kind of answer:

• Identify / State: a word or short phrase, no explanation needed.
• Calculate: show the formula, substitute, and give a labelled numerical answer (with units or a percent sign).
• Draw / Show / Use a graph: produce a fully labelled diagram that responds exactly to the prompt.
• Explain: give a cause-and-effect chain ("because X, then Y, so Z"), not just a restatement.

Answer each lettered part in order, keep prose tight, and let the graph carry any "show" task.

A study sequence that works

Build the skills in this order so each rests on the last:

1. Definitions first. Lock down scarcity, opportunity cost, the laws of demand and supply, and the cost and revenue concepts.
2. The Unit 2 market graph. Draw supply and demand until labelling is automatic, then drill single and double shifts, elasticity, and surplus.
3. The firm graphs. Master the cost curves, then the perfect competition, monopoly, and monopolistic competition diagrams, especially the two-step price method.
4. Factor markets and externalities. Add the MRP and monopsony graphs and the externality (private versus social) diagrams.
5. Timed free-response practice. Work released-style questions under time, then check your graphs and calculations against the scoring logic.

Check your technique

A mix of graphing, calculation, and reasoning questions covering the core exam skills. Attempt them under timed conditions, then check against the solutions.

1. State the two things you must label on the axes of a supply and demand graph. (2 marks)
2. A good's own price falls. State whether this is a movement along or a shift of the demand curve. (1 mark)
3. A price rises from $8 to$12 and quantity demanded falls from 600 to 400. Using the midpoint formula, calculate the price elasticity of demand. (2 marks)
4. A monopolist's MR = MC at 40 units; demand at 40 units is $18 and ATC is$12. Calculate total profit. (2 marks)
5. Both demand and supply increase (both shift right). State which of price and quantity is indeterminate. (2 marks)
6. A worker's marginal product is 6 and the product sells competitively at $7. Calculate the marginal revenue product. (1 mark)
7. State where the monopsony wage is read from once employment is set. (1 mark)
8. A prompt says "Explain why the equilibrium price rises." State what kind of answer the verb Explain requires. (1 mark)