AP Macroeconomics Basic Economic Concepts — Worked Answer Explanations

Unit 1 · 12 questions explained

Below is a complete answer key for our AP Macroeconomics 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
A country can produce either 100 units of wheat or 50 units of cloth per day. If it currently produces 80 units of wheat, what is the opportunity cost of producing the 80th unit of wheat?
- A
  0.5 units of clothCorrect
- B
  2 units of cloth
  Why not B: This inverts the ratio; if 100 wheat = 50 cloth, then 1 wheat costs 0.5 cloth, not 2.
- C
  1 unit of cloth
  Why not C: A 1-for-1 ratio would require equal maximum outputs, which is not the case here.
- D
  50 units of cloth
  Why not D: 50 units is the total cloth foregone if all resources go to wheat, not the per-unit opportunity cost.
Explanation
Opportunity cost per unit = $\frac{max cloth}{max wheat} = \frac{50}{100} = 0.5$ units of cloth per unit of wheat. This ratio is constant along a linear PPC, so every wheat unit costs 0.5 cloth regardless of current output.

Key takeaway
On a linear PPC, opportunity cost is constant and equals the slope ratio of maximum outputs.
Question 2 · Easy
Which of the following best illustrates the economic concept of scarcity?
- A
  A government imposes a price ceiling on gasoline.
  Why not A: A price ceiling is a policy response to prices, not an illustration of the fundamental scarcity problem itself.
- B
  Human wants exceed the resources available to satisfy them.Correct
- C
  A firm earns zero economic profit in the long run.
  Why not C: Zero economic profit describes a market equilibrium outcome, not the fundamental resource constraint of scarcity.
- D
  A consumer buys fewer goods when income falls.
  Why not D: This describes the income effect on demand, not the concept of scarcity itself.
Explanation
Scarcity is the fundamental economic problem: unlimited human wants face limited resources (land, labor, capital, entrepreneurship). Because resources are finite, every choice involves a trade-off.

Key takeaway
Scarcity arises because unlimited wants exceed limited resources, forcing trade-offs and choices.
Question 3 · Easy
A point located inside (below) the production possibilities curve (PPC) indicates that an economy is:
- A
  Operating at full efficiency with no unused resources.
  Why not A: Full efficiency corresponds to a point on the PPC, not inside it.
- B
  Producing an output combination that is currently unattainable.
  Why not B: Unattainable combinations lie outside (beyond) the PPC, not inside it.
- C
  Using resources inefficiently or leaving some resources unemployed.Correct
- D
  Experiencing economic growth that has shifted the PPC outward.
  Why not D: An outward PPC shift represents growth; a point inside the current PPC indicates inefficiency, not growth.
Explanation
Points inside the PPC are attainable but inefficient — the economy is not using all available resources productively (e.g., cyclical unemployment, idle capital). Points on the PPC represent full efficiency; points outside are currently unattainable.

Key takeaway
Inside PPC = inefficiency or unemployment. On PPC = full efficiency. Outside PPC = currently unattainable (requires growth).
Question 4 · Easy
If the price of coffee rises significantly, what is the most likely effect on the demand for tea, a substitute good?
- A
  Demand for tea decreases, shifting the demand curve left.
  Why not A: If coffee becomes more expensive, consumers switch to tea — demand for tea rises, not falls.
- B
  Demand for tea increases, shifting the demand curve right.Correct
- C
  The supply of tea increases, shifting the supply curve right.
  Why not C: A change in the price of a substitute affects demand (consumer behavior), not the supply side of the tea market.
- D
  There is no effect on the tea market because markets are independent.
  Why not D: Substitute goods are related markets; a price change in one shifts demand in the other.
Explanation
Tea and coffee are substitutes — consumers can use either to satisfy a similar want. When the price of coffee rises, coffee becomes relatively more expensive, so consumers substitute toward tea, increasing demand for tea (rightward shift of the demand curve).

Key takeaway
For substitute goods, a price increase in good X shifts the demand curve for good Y to the right.
Question 5 · Easy
Country Alpha can produce 10 cars or 20 tons of grain per worker-day. Country Beta can produce 6 cars or 18 tons of grain per worker-day. According to the principle of comparative advantage, which country should specialize in cars?
- A
  Alpha, because it has absolute advantage in both goods.
  Why not A: Absolute advantage does not determine specialization; comparative advantage (lower opportunity cost) does.
- B
  Alpha, because its opportunity cost of a car is 2 tons of grain, lower than Beta's 3 tons.Correct
- C
  Beta, because it produces fewer cars and should focus on improving.
  Why not C: Countries specialize where their opportunity cost is lowest, not where output is lowest.
- D
  Beta, because its opportunity cost of grain is lower.
  Why not D: Beta's lower opportunity cost in grain means Beta should specialize in grain, not cars.
Explanation
Alpha's opportunity cost of 1 car = $\frac{20}{10} = 2$ tons of grain. Beta's opportunity cost of 1 car = $\frac{18}{6} = 3$ tons of grain. Alpha has the lower opportunity cost in cars, so Alpha has comparative advantage in cars and should specialize there.

Key takeaway
Comparative advantage is determined by lower opportunity cost, not higher absolute output. Each country specializes where its opportunity cost is smallest.
Question 6 · Easy
The law of increasing opportunity costs suggests that a PPC is bowed outward (concave to the origin) because:
- A
  Resources are perfectly interchangeable between all uses.
  Why not A: Perfect interchangeability produces a linear PPC with constant opportunity costs, not an outward bow.
- B
  Resources are not equally productive in all uses, so shifting them grows increasingly costly.Correct
- C
  Technology improves as more of a good is produced.
  Why not C: Improved technology would shift the PPC outward, not explain its concave shape.
- D
  Demand for each good increases as the economy grows.
  Why not D: The shape of the PPC reflects resource constraints and productivity, not demand conditions.
Explanation
Resources are specialized — a wheat farmer is not equally productive making cloth. As more cloth is produced, increasingly unsuitable resources (e.g., grain-focused workers) must be redirected, raising the opportunity cost of each additional unit of cloth. This increasing opportunity cost creates the outward bow.

Key takeaway
Outward-bowed PPC reflects increasing opportunity costs due to resource specialization — resources are not perfectly interchangeable.
Question 7 · Easy
A decrease in the price of steel (an input to car production) will most likely:
- A
  Shift the demand curve for cars to the right.
  Why not A: Input price changes affect producers (supply side), not the tastes or incomes of car buyers (demand side).
- B
  Shift the supply curve for cars to the right, lowering the equilibrium price.Correct
- C
  Shift the supply curve for cars to the left, raising the equilibrium price.
  Why not C: A lower input cost reduces production costs, making it more profitable to supply cars — supply increases (rightward shift), not decreases.
- D
  Have no effect on the car market because steel and cars are in different industries.
  Why not D: Steel is an input to cars; cheaper inputs reduce production costs and increase supply.
Explanation
A fall in the price of steel reduces car manufacturers' production costs. Lower costs increase profitability at every price level, shifting the supply curve for cars to the right. This increases equilibrium quantity and lowers equilibrium price, all else equal.

Key takeaway
A decrease in input prices shifts the supply curve right (increases supply), lowering equilibrium price and raising equilibrium quantity.
Question 8 · Easy
Two countries can both gain from trade even if one country has an absolute advantage in producing all goods. This is explained by:
- A
  The principle of absolute advantage — the more productive country always benefits.
  Why not A: Absolute advantage alone cannot explain mutual gains; comparative advantage — based on opportunity costs — is the correct explanation.
- B
  The principle of comparative advantage — each country specializes in the good where its opportunity cost is lower.Correct
- C
  The terms of trade, which always equalize wages across countries.
  Why not C: Terms of trade determine how gains are divided, not whether gains exist; wage equalization is a separate prediction not required for mutual gains.
- D
  Economies of scale, which reduce costs as output expands.
  Why not D: Economies of scale can reinforce trade gains but are not the fundamental reason both countries benefit; comparative advantage is.
Explanation
Even if Country A produces more of everything per worker (absolute advantage), Country B may have a lower opportunity cost in one good. By each specializing in their comparative advantage and trading, total output rises and both can consume more than in autarky.

Key takeaway
Comparative advantage — not absolute advantage — drives mutually beneficial specialization and trade.
Question 9 · Medium
In a competitive market, the price of good X rises. Which of the following best describes what happens to producer surplus?
- A
  Producer surplus decreases because higher prices deter consumers.
  Why not A: Higher prices benefit producers (revenue rises above minimum willingness to accept); consumer deterrence affects consumer surplus, not producer surplus directly.
- B
  Producer surplus increases because sellers receive more above their minimum acceptable price.Correct
- C
  Producer surplus is unchanged because the supply curve does not shift.
  Why not C: Even with an unchanged supply curve, a higher price increases the area between price and the supply curve, so producer surplus rises.
- D
  Producer surplus decreases because quantity supplied increases, raising costs.
  Why not D: While quantity and costs rise, the higher price more than compensates, so the surplus (area above supply, below price) expands.
Explanation
Producer surplus is the area above the supply curve and below the market price. When price rises, this area expands in two ways: each existing unit earns more surplus, and new units are produced that also contribute positive surplus. Net effect: producer surplus increases.

Key takeaway
Producer surplus = area above supply curve, below price. A higher price increases producer surplus.
Question 10 · Medium
In a market with a binding price floor set above equilibrium, which of the following outcomes is most likely?
- A
  A shortage, because quantity demanded exceeds quantity supplied at the floor price.
  Why not A: A price floor above equilibrium raises price, causing quantity supplied to exceed quantity demanded — a surplus, not a shortage. Shortages arise from price ceilings below equilibrium.
- B
  A surplus, because quantity supplied exceeds quantity demanded at the floor price.Correct
- C
  No effect, because markets always clear at the equilibrium price.
  Why not C: Markets clear only when price is at equilibrium; a binding floor forces price above equilibrium, creating a surplus.
- D
  A decrease in supply, as producers find the good unprofitable.
  Why not D: A price floor above equilibrium raises the price sellers receive, making production more attractive — supply does not decrease.
Explanation
A binding price floor sets the legal minimum price above the equilibrium price. At this higher price, producers want to supply more and consumers want to buy less, creating a surplus (excess supply). Classic example: agricultural price floors create grain surpluses.

Key takeaway
Price floor above equilibrium → surplus (quantity supplied > quantity demanded). Price ceiling below equilibrium → shortage.
Question 11 · Medium
An economy currently produces at a point on its PPC. Technological improvement occurs only in the production of manufactured goods. How does the PPC shift?
- A
  The entire PPC shifts outward proportionally.
  Why not A: A proportional outward shift requires improvement in producing all goods equally; a sector-specific advance rotates or pivots the PPC.
- B
  The PPC rotates outward along the manufactured-goods axis only.Correct
- C
  The PPC shifts inward along the manufactured-goods axis.
  Why not C: Technological improvement increases productive capacity, shifting the relevant axis outward, not inward.
- D
  The PPC does not change because no new resources were added.
  Why not D: Technology improvements can shift the PPC even without adding new resources by increasing output per existing resource.
Explanation
When technology improves only in manufactured goods, the maximum possible output of manufactured goods increases while the maximum output of other goods is unchanged. The PPC pivots (rotates) outward along the manufactured-goods axis, creating a new larger intercept on that axis while the other intercept stays fixed.

Key takeaway
Sector-specific technology improvement pivots the PPC outward along that sector's axis; economy-wide improvement shifts the entire PPC outward.
Question 12 · Medium
Country A's opportunity cost of producing 1 unit of wheat is 3 units of cloth. Country B's opportunity cost of producing 1 unit of wheat is 2 units of cloth. Which of the following trade arrangements could benefit both countries?
- A
  Country A exports wheat to Country B at a rate of 4 cloth per wheat.
  Why not A: Country B has comparative advantage in wheat (lower opportunity cost of 2 cloth per wheat). Country A should export cloth, not wheat.
- B
  Country B exports wheat to Country A at a rate of 2.5 cloth per wheat.Correct
- C
  Country A exports wheat to Country B at a rate of 1.5 cloth per wheat.
  Why not C: 1.5 cloth per wheat is below Country B's opportunity cost of 2, so B gains nothing from this trade — it can produce wheat more cheaply itself.
- D
  No trade is beneficial because Country B has lower opportunity costs.
  Why not D: Country A has comparative advantage in cloth (its cloth opportunity cost = 1/3 wheat, vs. B's 1/2 wheat). Both can gain by Country B specializing in wheat and A in cloth.
Explanation
Country B has comparative advantage in wheat (opportunity cost: 2 cloth per wheat < A's 3 cloth per wheat). Country A has comparative advantage in cloth. For mutually beneficial trade, the terms of trade must lie between the two countries' opportunity costs: between 2 and 3 cloth per wheat. A rate of 2.5 cloth per wheat falls in this range, so both benefit.

Key takeaway
Mutually beneficial terms of trade lie strictly between the two countries' opportunity costs — each country gains relative to producing the good itself.