Study guide: Microeconomics Models and Decisions
Calculate costs, compare opportunity costs and interpret market conditions.
Ideas to explain in your own words
- Revenue is the amount received from sales. Cost records resources paid for production. In the fictional one-product model, profit equals revenue minus total cost, with revenue equal to price times units sold. Profit is not the same as cash balance, and the model omits taxes and other business complexities.
- Comparative advantage concerns lower opportunity cost, not simply larger output. The fictional model assumes fixed resources and a straight-line, constant trade-off between two endpoint outputs. The opportunity cost of one poster equals forgone cards divided by possible posters. Compare ratios using the same unit before discussing specialization.
- In a simple market model, equilibrium occurs where quantity supplied equals quantity demanded. A shortage means quantity demanded exceeds quantity supplied at the stated price; a surplus means the reverse. A shift changes a schedule, while movement along a schedule responds to its price. These are conditional models, not trading predictions.
- An externality is a cost or benefit affecting people outside the stated transaction. Private cost concerns the participant’s own expense; external cost affects others; external benefit helps others; a policy response changes incentives or rules. Identifying an external effect is not enough to prove one policy is best.
Useful vocabulary
- Input
- the values supplied for the stated model
- Rule
- the operation linking inputs to the result
- Input
- the values supplied for the stated model
- Rule
- the operation linking inputs to the result
- Equilibrium
- quantity supplied equals quantity demanded at the stated price
- Shortage
- quantity demanded exceeds quantity supplied at the stated price
- Private cost
- a cost borne by the stated transaction participant
- External cost
- a cost affecting others outside the stated transaction
Watch your reasoning
- Treating Total Revenue Cost and Profit as identical to Comparative Advantage and Opportunity Cost; check the distinct feature each lesson teaches.
- Extending one supplied example or model to every person, place or period without matching evidence. Compare affected parties and alternatives before recommending a policy.
A worked review example
Fictional price $5, sold 8 units, total cost $27. First find revenue: $5 × 8 = $40. Then subtract total cost: $40 − $27 = $13 profit. Reporting $40 would confuse revenue with profit; adding the cost would reverse the rule. The calculation uses only the supplied price, sales and cost. It does not establish cash balance, tax liability or a real business forecast.
Make a practice plan
- Review the factual notes for Total Revenue Cost and Profit and explain its defining distinction.
- Complete the main checks and three practice questions in each of the four lessons; write a reason, operation or evidence limit before checking.
- Use the review questions to diagnose the specific lesson needing practice, then retry it with the changed-input extension.
- Write the unit transfer task before attempting its separate cumulative questions.