Basic Economic Concepts

What this unit covers

The topics below follow the published Macro course framework for Unit 1. This unit is worth 5–10% of the exam, so budget your time against that rather than against how long the unit takes to teach.

Lessons in this unit

• Scarcity & Opportunity Cost13 min · 3 objectivesExplain why scarcity forces every society to make choices · Define opportunity cost as the value of the next-best alternative forgone · Apply marginal (cost–benefit) thinking to an economic decision
• The Production Possibilities Curve14 min · 3 objectivesInterpret a production possibilities curve as a model of scarcity, trade-offs, and efficiency · Explain why the PPC is typically bowed outward using the law of increasing opportunity cost · Distinguish movements along the PPC from shifts caused by growth
• Comparative Advantage & Gains from Trade14 min · 3 objectivesDistinguish absolute advantage from comparative advantage · Calculate opportunity costs from output or input data to determine comparative advantage · Identify mutually beneficial terms of trade using the gains from specialization
• Resource Allocation, Economic Systems & the Circular Flow14 min · 3 objectivesIdentify the three questions every economic system must answer · Compare how market, command and mixed systems allocate resources · Trace money, goods and resources through the circular flow model
• Terms of Trade: Who Gains, and by How Much15 min · 3 objectivesDistinguish output problems from input problems when computing opportunity cost · Determine the range of mutually beneficial terms of trade · Explain why absolute advantage is irrelevant to whether trade is beneficial
• Cost–Benefit Analysis & Marginal Decision Rules13 min · 3 objectivesApply the rule that a rational actor continues an activity while marginal benefit exceeds marginal cost · Explain why sunk costs are irrelevant to a forward-looking decision · Distinguish marginal from average and total quantities
• Consumer Choice & Utility Maximization13 min · 3 objectivesState the law of diminishing marginal utility and its effect on demand · Apply the utility-maximizing rule that equalizes marginal utility per dollar · Explain how a price change redirects spending toward the cheaper good

Formulas in Unit 1

Every term in Unit 1

All 42 terms we publish for Basic Economic Concepts, 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.

Scarcity

Wants exceed the resources available to satisfy them. The reason every economic question is a question about trade-offs, and the premise the whole course rests on.

Opportunity cost

The value of the next-best alternative given up. Not the money spent — the thing forgone. On the exam it is almost always measured in units of the other good.

Trade-off vs opportunity cost

A trade-off is all the alternatives given up; the opportunity cost is only the single best of them. Answers that list every forgone option do not earn the point.

Factors of production

Land, labor, capital and entrepreneurship. Payments to them are rent, wages, interest and profit — which is why the resource market mirrors the product market.

Production possibilities curve (PPC)

All combinations of two goods an economy can produce using its resources fully and efficiently. Points inside are attainable but inefficient; points outside are unattainable with current resources.

Why the PPC bows outward

Resources are not equally suited to both goods. Shifting the least-suited resources first is cheap; shifting the best-suited ones later is expensive — which is increasing opportunity cost.

A straight-line PPC

Means constant opportunity cost: resources are perfectly substitutable between the two goods. Slope equals the constant trade-off ratio.

Movement along vs shift of the PPC

Moving along it is reallocating existing resources and always costs something. Shifting it outward means more resources or better technology — growth, not reallocation.

Causes of outward PPC shifts

More resources, better technology, improved human capital, or institutions that raise productivity. A shift in only one axis means the gain applies to only one good.

Efficiency (productive)

Producing at the lowest possible cost — anywhere on the PPC. Points inside are productively inefficient because output is being left on the table.

Efficiency (allocative)

Producing the combination society most wants. Only one point on the PPC is allocatively efficient; being on the curve is not enough.

Absolute advantage

Producing more of a good with the same resources, or the same output with fewer. It does not determine who should specialize.

Comparative advantage

Producing a good at lower opportunity cost. This — not absolute advantage — determines the pattern of specialization and trade.

Finding comparative advantage from an output table

Divide the other good by this good ("other over"): the opportunity cost of one unit of good A is (units of B) / (units of A). Lower number wins.

Finding comparative advantage from an input table

With inputs per unit, the ratio flips — the country needing fewer hours per unit has the absolute advantage, and you still compare opportunity-cost ratios, not the raw inputs.

Terms of trade

An exchange rate between two goods that both parties accept. It must lie between the two countries' opportunity costs, or one of them gains nothing by trading.

Gains from trade

Specializing by comparative advantage and trading lets both countries consume beyond their own PPCs. The PPC does not move — the consumption point does.

Marginal analysis

Do one more unit while marginal benefit exceeds marginal cost; stop where MB = MC. Every optimization in the course is a version of this rule.

Positive vs normative statements

Positive statements can be tested against evidence; normative statements assert what ought to be. Free-response prompts asking you to "explain" want positive analysis.

Ceteris paribus

Holding all else constant. It is what allows a two-dimensional graph to isolate one relationship, and it is why a shift and a movement along a curve are different events.

The three questions every system answers

What to produce, how to produce it, and for whom. Systems differ only in who decides — market, command or mixed.

What prices do, precisely

Two jobs at once: they signal relative scarcity and they reward whoever responds. That is why a market coordinates without a coordinator.

Circular flow: product vs resource market

Product market — households pay firms for goods. Resource market — firms pay households for labor, land and capital. Money one way, real things the other.

Why total spending equals total income

An accounting identity forced by the circular flow: every dollar spent arrives at a firm and is paid out as wages, rent, interest or profit. Hence GDP can be measured two ways.

Leakages and injections

Saving, taxes and imports leak out of the direct loop; investment, government spending and exports inject back in. These are exactly the components of AD.

Output problem vs input problem

Output table (how much you can make): opportunity cost = other over own. Input table (hours per unit): own over other. The ratios INVERT between the two.

Absolute vs comparative advantage

Absolute: producing more with the same resources. Comparative: producing at lower opportunity cost. Only the second determines who specializes.

Why a country good at everything still trades

Comparative advantage compares ratios, so if one ratio is lower the other must be higher. No country can hold a comparative advantage in both goods.

Terms of trade range

A trade benefits both sides only when the exchange rate lies strictly between the two countries' opportunity costs. Outside that range, one party prefers self-sufficiency.

The marginal decision rule

Continue while MB > MC; stop where MB = MC. Not where total benefit is largest — total keeps rising while marginal benefit is positive.

Sunk cost

A cost already incurred and unrecoverable. Identical under every option, so it cannot distinguish them and must be ignored.

Marginal vs average vs total

Total is the running sum, average is total over quantity, marginal is the change from one more unit. Marginal can fall while average still rises.

Diminishing marginal utility

Each additional unit of the same good adds less satisfaction. This is why demand slopes down — extra units are only worth buying at a lower price.

Utility maximization rule

MU_x/P_x = MU_y/P_y with the whole budget spent. Equalize satisfaction per DOLLAR, not per unit.

Substitution vs income effect

A price cut makes the good relatively cheaper (substitution) and frees purchasing power (income). Both raise quantity demanded for a normal good.

Physical vs human capital

Physical capital is equipment and structures; human capital is the skills and knowledge workers carry. Both raise productivity and both shift LRAS right.

Points inside, on and outside the PPC

Inside is inefficient — unemployed or misallocated resources. On the curve is efficient. Outside is unattainable with current resources and technology.

What shifts the PPC

More resources, better technology, more human capital. The same list that shifts LRAS right — the PPC and LRAS are the same idea in different units.

Growth versus efficiency

Moving from inside the PPC to the curve is an efficiency gain; moving the curve itself outward is growth. Closing an output gap is the first, raising potential output the second.

Productive vs allocative efficiency

Productive: on the PPC, no output wasted. Allocative: at the point on the PPC society actually values most. Being efficient in the first sense says nothing about the second.

Normative vs positive statements

Positive statements are testable claims about what is; normative statements are judgments about what ought to be. Exams test the distinction because policy questions blur it.

Why economics uses models

Deliberate simplification to isolate one mechanism. A model is judged by whether its predictions hold, not by whether its assumptions are literally true.

What examiners penalize here

• When a free-response question asks for the "opportunity cost" of a policy or choice, name the specific forgone alternative and, where possible, quantify it. Vague answers like "you lose money" do not earn the point — identify *what* is given up.
• Label PPC diagrams precisely: axes for the two goods, a point *on* the curve for efficiency, a point *inside* for unemployment, and a *shifted* curve for growth. Graders award points for correct labeling and the correct type of change (movement vs. shift).
• On comparative-advantage problems, always compute opportunity costs first, then remember the shortcut for output tables: "Other over Own." Mixing up output and input data is the most common error — with **input** data (time or resources per unit) the ratio flips to "Own over Other."
• The circular flow rarely appears as its own free-response question, but it is the reason the GDP identity works and the reason leakages and injections must balance. Understanding it turns several later topics from memorization into deduction.
• Write the two opportunity costs in a small table before answering anything, labeled with units ("1 machine = 2 rice"). Free-response rubrics award the opportunity-cost calculation separately from the conclusion, so a correct table earns points even if you then name the wrong country.
• When a table of totals appears, write the marginal column in the margin before reading the question. Nearly every quantitative decision item is answered from that column, and computing it once beats recomputing differences under time pressure.
• Utility tables on the exam are almost always built so that a clean bundle exactly exhausts the budget. If your answer leaves money unspent or overspends, recheck the per-dollar column before doubting the arithmetic.

Practice Macro

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

All 6 units of AP Macroeconomics

1. Unit 1 · Basic Economic Concepts
2. Unit 2 · Economic Indicators & Business Cycle
3. Unit 3 · National Income & Price Determination
4. Unit 4 · Financial Sector
5. Unit 5 · Long-Run Consequences of Policy
6. Unit 6 · Open Economy