Microeconomics Foundations (ECON 101) · Module 1 of 9
Scarcity, Opportunity Cost & the PPF
The foundational trade-offs every economy faces, and why specialization makes everyone better off.
Scarcity & Opportunity Cost
- Scarcity means resources are limited relative to unlimited wants, forcing every economic choice to involve a trade-off.
- Opportunity cost is the value of the next best alternative given up when making a choice — the true, real cost of any decision, not just its stated price.
If you choose to spend an evening studying instead of working a part-time shift that pays $60, what is the opportunity cost of studying?
Solution. The $60 in wages given up (plus anything else that shift would have provided) is the opportunity cost of choosing to study instead.
The Production Possibilities Frontier (PPF)
- The PPF shows the maximum combinations of two goods an economy can produce with fixed resources and technology, given full and efficient use of those resources.
- Points inside the PPF represent inefficient use of resources; points outside are currently unattainable; points on the curve are efficient trade-offs.
- The PPF's outward bow shape (concave from the origin) reflects increasing opportunity cost — resources aren't equally well-suited to producing both goods.
What does a point lying inside (not on) the PPF indicate about an economy?
Solution. It indicates the economy is producing inefficiently — not fully utilizing its available resources or technology — since it could produce more of at least one good without producing less of the other.
Comparative Advantage & Gains from Trade
- Absolute advantage means producing more of a good with the same resources; comparative advantage means having a lower opportunity cost of producing that good compared to someone else.
- Trade benefits both parties when each specializes in producing the good in which they have a comparative advantage, even if one party has an absolute advantage in everything.
Why can trade benefit two countries even if one country is better at producing everything (has an absolute advantage in both goods)?
Solution. What matters for trade is comparative advantage — the relative opportunity cost of producing each good — not absolute advantage; even a country that is better at producing everything still has a lower opportunity cost in one good relative to the other, and specializing based on that lets both countries gain from trade.
Economic Systems & the Three Basic Questions
- Every economy must answer three basic questions: what to produce, how to produce it, and for whom to produce it.
- Market economies answer these questions primarily through price signals and individual choices; command economies rely on centralized government planning.
How does a market economy typically decide "what to produce"?
Solution. Primarily through price signals: if consumers demand more of a good, its price rises, signaling producers to supply more of it, and vice versa — decisions emerge from the decentralized choices of buyers and sellers rather than central planning.
Check yourself
2 of this module's 5 quiz questions. Pick your answers, then check them in the app, with an explanation for every question.
1. What is opportunity cost?
2. What does a point on the PPF (not inside it) represent?