AP Microeconomics Basic Economic Concepts — Worked Answer Explanations

Unit 1 · 12 questions explained

Below is a complete answer key for our AP Microeconomics Basic Economic Concepts practice questions. For each question you'll find the correct choice, a full written explanation of how to get there, and — for every wrong answer — a short note on exactly why it's tempting and where it goes wrong. Reading these straight through is one of the fastest ways to find the gaps in a unit before exam day.

Prefer to test yourself first? Take the timed Basic Economic Concepts practice test and come back here to review, or head back to the Basic Economic Concepts unit overview.

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Question 1 · Easy
An economy currently operates inside its production possibilities curve (PPC). This situation most likely indicates that the economy is experiencing:
- A
  Efficient allocation of all available resources.
  Why not A: Efficient allocation of resources corresponds to a point on the PPC, not inside it.
- B
  Unemployment or underutilization of resources.Correct
- C
  A point that is technologically impossible to achieve.
  Why not C: Points outside the PPC are currently unattainable. Points inside are attainable but inefficient.
- D
  An outward shift in the production possibilities curve.
  Why not D: Operating inside the PPC does not shift the curve. An outward shift requires more resources or improved technology.
Explanation
The PPC represents maximum output combinations using all resources fully and efficiently. A point inside the PPC means the economy is not using all its resources (unemployment) or is using them inefficiently (underutilization). Points on the PPC are productively efficient; points outside are currently unattainable without economic growth.

Key takeaway
Inside the PPC = underutilization or unemployment; on the PPC = productive efficiency; outside = unattainable without growth.
Question 2 · Easy
Which of the following is the best example of a marginal decision?
- A
  A firm decides whether to enter a new industry.
  Why not A: This is a long-run structural decision, not a marginal unit-by-unit decision.
- B
  A government sets a national budget for the next fiscal year.
  Why not B: Budget-setting is a broad policy decision rather than an incremental 'one more unit' analysis.
- C
  A student decides whether to study one additional hour for a test.Correct
- D
  A country chooses between a market economy and a command economy.
  Why not D: Choosing an economic system is a sweeping institutional decision, not a marginal cost-benefit comparison at the unit level.
Explanation
Marginal analysis compares the additional (marginal) benefit of one more unit of an activity against the additional (marginal) cost. Deciding whether to study one more hour fits this exactly: the student weighs the extra benefit (higher test score) against the extra cost (time, fatigue). The other choices involve broad, all-or-nothing decisions rather than incremental unit comparisons.

Key takeaway
Marginal decisions ask 'one more unit?' — weighing marginal benefit against marginal cost at the margin.
Question 3 · Easy
The concept of scarcity in economics refers to the condition in which:
- A
  Only low-income individuals cannot afford the goods they want.
  Why not A: Scarcity is universal and applies to all individuals and societies, not just low-income groups.
- B
  Resources are insufficient to satisfy all human wants simultaneously.Correct
- C
  Goods are physically rare or difficult to find in nature.
  Why not C: Scarcity is an economic concept about wants exceeding available resources, not about physical rarity. Air is abundant physically but time to enjoy it may be scarce.
- D
  A country lacks the technology to produce enough goods for its population.
  Why not D: Technology is just one resource that affects scarcity. Even highly developed nations with advanced technology face scarcity because wants are unlimited.
Explanation
Scarcity is the fundamental economic problem: human wants are unlimited while resources (land, labor, capital, entrepreneurship) are finite. This gap exists in every society regardless of wealth or technology level, forcing all economic actors to make choices — and every choice has an opportunity cost. Scarcity is not the same as poverty or physical rarity.

Key takeaway
Scarcity = unlimited wants + limited resources; it exists in every economy and forces trade-offs.
Question 4 · Easy
A student can produce either 10 essays or 20 problem sets per week, while a tutor can produce either 30 essays or 45 problem sets per week. Which of the following correctly identifies the comparative advantage of each person?
- A
  The student has a comparative advantage in essays; the tutor has a comparative advantage in problem sets.Correct
- B
  The tutor has a comparative advantage in both essays and problem sets.
  Why not B: Having absolute advantage in both goods does not mean having comparative advantage in both — comparative advantage is determined by the lower opportunity cost, not total output.
- C
  The student has a comparative advantage in problem sets; the tutor has a comparative advantage in essays.
  Why not C: The student's opportunity cost of 1 essay is 2 problem sets, while the tutor's is 1.5 problem sets. The tutor has the lower opportunity cost for essays, giving the tutor comparative advantage there.
- D
  Neither person has a comparative advantage because the tutor is better at everything.
  Why not D: Comparative advantage always exists unless opportunity costs are exactly equal. Absolute advantage in all goods does not eliminate comparative advantage.
Explanation
The student's opportunity cost of 1 essay is $\frac{20}{10} = 2$ problem sets. The tutor's opportunity cost of 1 essay is $\frac{45}{30} = 1.5$ problem sets. Since the tutor has a lower opportunity cost for essays, the tutor has comparative advantage in essays. The student has comparative advantage in problem sets (opportunity cost = 0.5 essays vs. the tutor's $\frac{30}{45} \approx 0.67$ essays).

Key takeaway
Comparative advantage belongs to whoever has the lower opportunity cost, regardless of absolute productivity levels.
Question 5 · Easy
A linear PPC has endpoints at (0, 80) for Good Y and (40, 0) for Good X. What is the opportunity cost of producing one additional unit of Good X?
- A
  $\frac{1}{2}$ unit of Good Y
  Why not A: This inverts the ratio; the slope from X to Y is 80/40 = 2, not 1/2.
- B
  2 units of Good YCorrect
- C
  40 units of Good Y
  Why not C: 40 is the maximum output of X, not the per-unit opportunity cost.
- D
  80 units of Good Y
  Why not D: 80 is the maximum output of Y, representing the total opportunity cost of producing all 40 units of X — not one unit.
Explanation
On a linear PPC, opportunity cost is constant and equals the slope. Moving from (0, 80) to (40, 0) means gaining 40 units of X while giving up 80 units of Y. The opportunity cost per unit of X is $\frac{80}{40} = 2$ units of Y. Because the PPC is linear, this rate is constant along the entire frontier.

Key takeaway
On a linear PPC, opportunity cost per unit = $\frac{\Delta Y}{\Delta X}$, and it is constant throughout.
Question 6 · Easy
A firm decides to keep operating a machine that cost $50, 000 tw oy e a r s a g o, e v e n t h o ug han e w er ma c hin e w o u l d p r o d u ceo u tp u t m or ec h e a pl y . F r o man eco n o mi cs t an d p o in t, t h e$ 50,000 is:
- A
  A variable cost that should factor into the decision to upgrade.
  Why not A: The original purchase price is a past expenditure — it has already been paid and cannot be changed by the current decision.
- B
  An opportunity cost that must be deducted from future revenue.
  Why not B: The sunk cost is not an opportunity cost of the upgrade decision; the opportunity cost consists of future benefits forgone.
- C
  A sunk cost that should not influence the upgrade decision.Correct
- D
  A fixed cost that reduces the firm's profit by $50,000 each year.
  Why not D: The $50,000 was spent in the past. It may be depreciated over time on accounting statements, but economically it is sunk and irrelevant to the marginal decision to upgrade.
Explanation
A sunk cost is any expenditure that has already been made and cannot be recovered. The $50,000 machine purchase is sunk: it was paid two years ago and the money is gone regardless of what happens next. Rational decision-making requires ignoring sunk costs and focusing only on future marginal costs and benefits. Keeping the old machine to 'get value out of it' is a classic sunk cost fallacy.

Key takeaway
Sunk costs are past and irretrievable — rational decisions ignore them and focus only on future costs and benefits.
Question 7 · Easy
If the marginal benefit of consuming a good is greater than its marginal cost, a rational individual should:
- A
  Stop consuming the good because costs are about to exceed benefits.
  Why not A: MB > MC means there is still a net gain from consuming more; stopping now leaves unrealized surplus on the table.
- B
  Consume more of the good until marginal benefit equals marginal cost.Correct
- C
  Consume less of the good to reduce total cost.
  Why not C: Reducing consumption when MB > MC sacrifices net gains; the rational move is to expand consumption, not contract it.
- D
  Ignore marginal costs and maximize total benefit instead.
  Why not D: Maximizing total benefit without regard to cost leads to over-consumption past the optimal point where MB = MC.
Explanation
The core principle of marginal analysis: continue any activity as long as its marginal benefit (MB) exceeds its marginal cost (MC). When $M B > M C$ , each additional unit adds more benefit than cost, increasing net surplus. The optimal quantity is reached at $M B = M C$ . Stopping short leaves potential gains unrealized; going beyond $M B = M C$ incurs more cost than benefit.

Key takeaway
Optimal quantity satisfies $MB = MC$; when $MB > MC$, expand; when $MB < MC$, contract.
Question 8 · Easy
Which of the following events would cause an outward (rightward) shift of an economy's PPC?
- A
  An increase in the unemployment rate.
  Why not A: Higher unemployment means the economy moves inside the existing PPC, not that the PPC itself shifts outward.
- B
  A reduction in consumer spending during a recession.
  Why not B: Changes in spending affect where the economy operates relative to the PPC (demand-side), not the position of the PPC itself.
- C
  An improvement in the education level of the labor force.Correct
- D
  A reallocation of workers from manufacturing to services.
  Why not D: Reallocation moves production along the existing PPC (changing the output mix), not outward.
Explanation
The PPC shifts outward when an economy's productive capacity increases — through more resources or better technology/human capital. Improving education raises the quality of labor (human capital), enabling greater total output from the same number of workers. This expands the frontier. In contrast, unemployment, spending cuts, and reallocation only affect where the economy operates within or along the existing PPC.

Key takeaway
PPC shifts out with more or better resources (including human capital) and improved technology; it doesn't shift from demand changes.
Question 9 · Medium
When a new technology improves the production of consumer goods but not capital goods, what happens to the PPC?
- A
  The PPC shifts outward uniformly along both axes.
  Why not A: A uniform outward shift occurs only when technology improves production of both goods equally.
- B
  The PPC rotates outward along the consumer goods axis only.Correct
- C
  The PPC shifts inward, reflecting that resources now have an alternative use.
  Why not C: Improved technology expands productive capacity; it does not reduce the PPC. Inward shifts occur due to resource loss or technology regression.
- D
  The PPC becomes linear because the opportunity cost is now constant.
  Why not D: A change in one sector's technology does not linearize the PPC; it creates asymmetric growth on one axis only.
Explanation
If technology improves only in the consumer goods sector, the maximum attainable output of consumer goods rises while the maximum output of capital goods is unchanged. Graphically, the endpoint on the consumer goods axis shifts outward while the capital goods axis endpoint stays fixed — this is a rotation (or pivot) of the PPC outward along the consumer goods axis. The curve becomes more bowed out, reflecting an asymmetric increase in potential.

Key takeaway
Sector-specific technology improvements rotate the PPC outward on the improved-good axis, not a parallel shift.
Question 10 · Medium
Country Alpha can produce 6 tons of wheat per labor-hour or 3 tons of steel per labor-hour. Country Beta can produce 4 tons of wheat per labor-hour or 4 tons of steel per labor-hour. Which statement is correct?
- A
  Alpha has comparative advantage in wheat; Beta has comparative advantage in steel.Correct
- B
  Alpha has comparative advantage in steel; Beta has comparative advantage in wheat.
  Why not B: Alpha's opportunity cost for steel is 2 tons of wheat, while Beta's is 1 ton of wheat — Beta has the lower opportunity cost for steel.
- C
  Alpha has absolute and comparative advantage in both goods.
  Why not C: Alpha has absolute advantage in wheat (6 > 4) but not steel (3 < 4). Comparative advantage in both goods cannot exist for one country.
- D
  No gains from trade are possible because Beta has equal productivity in both goods.
  Why not D: Equal internal opportunity costs for Beta (1:1 ratio) simply mean Beta is indifferent between goods, but gains from trade still arise from Alpha's different opportunity cost ratios.
Explanation
Alpha's opportunity cost of 1 ton of wheat = $\frac{3}{6} = 0.5$ tons of steel. Beta's opportunity cost of 1 ton of wheat = $\frac{4}{4} = 1$ ton of steel. Alpha has the lower opportunity cost for wheat (0.5 < 1), so Alpha has comparative advantage in wheat. Beta's opportunity cost of 1 ton of steel = $\frac{4}{4} = 1$ ton of wheat, vs Alpha's $\frac{6}{3} = 2$ tons of wheat. Beta has comparative advantage in steel. Gains from trade arise from these differing opportunity costs.

Key takeaway
Compare opportunity cost ratios across countries for each good to identify comparative advantage.
Question 11 · Medium
Trade between two parties occurs voluntarily only when:
- A
  One party has absolute advantage in producing every traded good.
  Why not A: Absolute advantage determines who is more productive overall, but it is not the condition that drives voluntary trade — comparative advantage is.
- B
  Both parties believe they will be better off from the exchange.Correct
- C
  The terms of trade equal the opportunity cost of the less productive party.
  Why not C: For mutually beneficial trade, the terms of trade must lie between the two countries' opportunity costs — not equal one party's cost.
- D
  A government regulator approves the exchange to ensure fairness.
  Why not D: Voluntary trade does not require government approval. Both parties self-select based on perceived mutual gain.
Explanation
Voluntary exchange is driven by mutual benefit: trade only happens when both parties expect to gain. This is guaranteed when each party specializes according to comparative advantage and trades at a price (terms of trade) that lies between their respective opportunity costs. At such terms of trade, both parties can consume outside their individual PPCs — a result that would be impossible through self-sufficiency alone.

Key takeaway
Voluntary trade occurs only when both parties gain; the terms of trade must fall between each party's opportunity costs.
Question 12 · Hard
A concave (bowed-out) PPC, as opposed to a linear one, reflects which economic principle?
- A
  Constant opportunity costs for each additional unit of a good produced.
  Why not A: Constant opportunity costs produce a linear PPC. A bowed-out PPC reflects rising opportunity costs.
- B
  The law of increasing opportunity costs due to resource specialization.Correct
- C
  Diminishing marginal utility of consumption rather than production constraints.
  Why not C: Diminishing marginal utility is a demand-side concept; the shape of the PPC reflects supply-side production trade-offs.
- D
  Economies of scale in producing both goods simultaneously.
  Why not D: Economies of scale would suggest falling costs as output rises, which could bow the PPC inward, not outward.
Explanation
A bowed-out (concave) PPC reflects the law of increasing opportunity costs: as production of one good increases, successively larger amounts of the other good must be sacrificed. This occurs because resources are not equally well-suited to producing all goods. Early on, resources well-suited to Good X are reallocated; later, increasingly specialized resources (better suited for Y) must be redirected, raising the per-unit cost. A linear PPC would imply resources are perfectly substitutable — constant opportunity costs.

Key takeaway
A bowed-out PPC reflects increasing opportunity costs caused by resource specialization; linear PPCs imply constant opportunity costs.