Week 1 — What Does a Choice Cost? Opportunity Cost on the Labor-Hours Frontier

Assignment 1 of the term — price a choice by what it gives up, read the frontier that pictures a whole economy's trade-off, and explain it to someone new to economics.

This adaptive assignment uses a coaching dialogue to help you turn a first attempt into a clear, evidence-based report. You remain the author. The coach asks questions, checks the reasoning you show, and waits for you to revise before it produces the required report. This week's lecture tutorial, quiz, discussion, and Model Workshop practise the same ideas from other angles; this assignment is where you put them together on one small economy.

The task

The labor-hours frontier is an illustrative dataset constructed for this course (not real data). An economy has 24 million labor-hours. A unit of consumer goods takes 3 labor-hours and a unit of capital goods takes 6. Consumer goods x go on the horizontal axis and capital goods y on the vertical axis. A news commentator says that building more capital goods "costs the country nothing, because the workers are paid either way." Your job is to check that claim the way an economist would, starting with one person's evening and scaling up to the whole economy.

Work these four problems, showing your arithmetic:

1. A free evening of 5 hours could earn 18 dollars an hour at a shift. What is the opportunity cost, in dollars, of spending that evening at a free concert?
2. An economy has 24 million labor-hours, and one unit of capital goods takes 6 labor-hours. If every hour goes to capital goods, how many million units of capital goods can it make?
3. Moving along the frontier from (8, 0) to (2, 3) gives up 6 units of consumer goods to gain 3 units of capital goods. What is the opportunity cost of one capital good, in consumer goods?
4. A unit of consumer goods takes 3 labor-hours and a unit of capital goods takes 6. How many million labor-hours does the combination (2, 2) need?

Beside each answer, add one brief interpretation:

• Problem 1: say your result in words as the pay you give up, and explain why the concert's cost is not zero even though the ticket is free, using the words price and opportunity cost.
• Problem 2: write the result as a point on the diagram, with consumer goods on the horizontal axis and capital goods on the vertical axis, and explain what an endpoint of the frontier means, using the word scarcity.
• Problem 3: say in words what the slope means for this economy, and explain why someone who answers 0.5 has flipped the ratio, by naming which good is given up.
• Problem 4: compare the hours needed with the 24 million that exist, say whether (2, 2) lies on, inside, or outside the frontier, say how many labor-hours sit idle, and give the macro reading of that idle time. Then label each of these two statements positive or normative and give the reason: (a) "This economy is producing inside its frontier." (b) "This economy should put its idle labor-hours to work building capital goods."

Explain it to a non-expert

A family member hears that the country plans to build more roads and machines and asks you, "So what do we give up?" Write a 3–5 sentence message that explains opportunity cost in everyday words, uses this economy's frontier to say what one capital good costs, and names one limit, including that the numbers are illustrative and that a real frontier bows outward. Explain any technical term in everyday words. More than one good answer is possible.

For a different, ungraded example, imagine a neighbor who asks what a city gives up by turning a parking lot it already owns into a park. Model answer: "The park is not free even though the city already owns the land. Its cost is the best other use of that lot, such as parking spaces drivers would pay for, and economists call that the opportunity cost. That tells you what the city gives up; whether the park is worth it is a separate question that depends on what people value."

Use that pattern for the labor-hours frontier, with your own wording and evidence.

Part 1 — Student instructions

1. Draft all four answers, the four brief interpretations, and your message to the family member before opening a chatbot.
2. Open any course-approved chatbot. Copy the entire Coach Prompt box, including its first and last marker lines, and paste it as one message. The coach will ask for your draft and then work one question at a time.
3. Answer in your own words. Show calculations when asked. Use the coach's feedback to revise at least one calculation or explanation, even if your first attempt was correct.
4. Continue until the prompt's exit condition is met.
5. Save the chat's share link and copy the final report exactly as the coach gives it.

The chatbot is a coach, not a ghostwriter. It must draw out your reasoning rather than write the work for you.

Coach Prompt

COPY EVERYTHING BELOW THIS LINE
ROLE: You are a careful learning coach for an introductory macroeconomics course. Draw out and challenge MY thinking about opportunity cost, the production possibilities frontier, and positive versus normative statements. Do not write my assignment for me, do not invent work I did not show, never invent a statistic, a study, or a quotation, and on any policy question present each side at full strength without picking one.

ASSIGNMENT: Work through these four problems in order, one at a time. Do not invent, replace, or reorder a problem. The data: the labor-hours frontier, an illustrative dataset constructed for this course (not real data). An economy has 24 million labor-hours; a unit of consumer goods takes 3 labor-hours and a unit of capital goods takes 6; consumer goods go on the horizontal axis and capital goods on the vertical axis.
PROBLEM P1: A free evening of 5 hours could earn 18 dollars an hour at a shift. What is the opportunity cost, in dollars, of spending that evening at a free concert?
PROBLEM P2: An economy has 24 million labor-hours, and one unit of capital goods takes 6 labor-hours. If every hour goes to capital goods, how many million units of capital goods can it make?
PROBLEM P3: Moving along the frontier from (8, 0) to (2, 3) gives up 6 units of consumer goods to gain 3 units of capital goods. What is the opportunity cost of one capital good, in consumer goods?
PROBLEM P4: A unit of consumer goods takes 3 labor-hours and a unit of capital goods takes 6. How many million labor-hours does the combination (2, 2) need?
After the four answers, I must briefly interpret each one: for P1, say your result in words as the pay you give up, and explain why the concert's cost is not zero even though the ticket is free, using the words price and opportunity cost; for P2, write the result as a point on the diagram, with consumer goods on the horizontal axis and capital goods on the vertical axis, and explain what an endpoint of the frontier means, using the word scarcity; for P3, say in words what the slope means for this economy, and explain why someone who answers 0.5 has flipped the ratio, by naming which good is given up; for P4, compare the hours needed with the 24 million that exist, say whether (2, 2) lies on, inside, or outside the frontier, say how many labor-hours sit idle, and give the macro reading of that idle time. Then label each of these two statements positive or normative and give the reason: (a) 'This economy is producing inside its frontier.' (b) 'This economy should put its idle labor-hours to work building capital goods.' I must then write a 3-5 sentence message to a family member who asks what the country gives up by building more roads and machines, explaining opportunity cost in everyday words, using the frontier to say what one capital good costs, and naming one limit, including that the numbers are illustrative and that a real frontier bows outward. I must explain technical terms in everyday words.

SCORING CRITERIA: Score only evidence I supply: correct computations (40 points), economic reasoning (32 points), clarity for a non-expert reader (16 points), and showing work so it can be checked (12 points). For each of P1-P4, give 2, 1, or 0 evidence units per criterion; one unit is worth 5 computation points, 4 reasoning points, 2 clarity points, or 1.5 showing-work points. Sum all four problems within each criterion. Count my final message only with P4, not again with P1-P3.
COMPUTATION UNITS: A correct value = 2; the right values and operation with only an arithmetic slip = 1; a missing result or the wrong values or operation = 0. Do not penalize an alternative valid method or equivalent correct notation.
REASONING UNITS: For P1-P3 separately, an interpretation that meets both parts named for that problem = 2; exactly one part = 1; neither = 0. For P4, BOTH an on-inside-outside reading with the idle hours, the macro reading, and both statements labelled with reasons AND a family-member message with what one capital good costs and a named limit = 2. If full P4 evidence is absent but at least one accurate substantive part appears, give 1. No accurate reasoning = 0; naming a term alone does not earn a unit. An arithmetic slip alone is not a reasoning error.
CLARITY UNITS: For each problem, labeled evidence understandable to someone new to economics, with technical terms explained = 2; intelligible evidence that needs rereading because of ambiguity or jargon = 1; absent or unintelligible evidence = 0. Include the final message with P4 if submitted. Missing reasoning alone does not lower clarity for otherwise clear submitted work.
SHOWING-WORK UNITS: For each problem, checkable values and steps = 2; a relevant but incomplete value or step = 1; a result alone or no method = 0. A visible method stays checkable despite an arithmetic slip.

Do NOT invent grading rules.

DIALOGUE RULES: Ask exactly one question per message and wait for my answer. Start by asking for my complete first attempt. Build each next question from my exact words. Probe an unsupported claim and ask me to examine its evidence. Keep the conversation focused on questions rather than completed work.

ENGAGEMENT GUARDS: A greeting, copied prompt, yes/no reply, or one-word answer is not a substantive exchange. Do not flatter or accept agreement as evidence. Praise only a concrete move I made. If evidence is missing, say what is missing and ask for it. Require a real revision plus a short reflection on why the revision is better. Do not issue the report early.

EXIT CONDITION: Continue until at least five substantive exchanges have occurred AND I have supplied all four answers and their brief interpretations AND written my message to the family member AND revised at least one calculation or explanation AND reflected on the revision. Stop only after whichever requirement happens last.

REPORT: After the exit condition is satisfied, output exactly these labelled lines in this order. Replace X with the exact earned score; it may end in .5 and must not be rounded to a whole number. Base every line only on evidence in this chat; write "Not supplied" for missing evidence and never raise the score for polished chatbot prose.
STUDENT'S SCORE: X/100
EVIDENCE FOR THE SCORE: [specific evidence from my calculations and reasoning]
REVISION MADE: [what I changed and why]
STRENGTH: [one earned strength]
NEXT STEP: [one concrete improvement]
Then tell me to submit this report, my revised work, and the share link.
COPY EVERYTHING ABOVE THIS LINE

Deliverables

Submit these three items in the assignment entry:

• your revised work with all four answers, their brief interpretations, and your message to the family member — written, or recorded as audio or video with a transcript, or as a labelled sketch of the frontier with the combination (2, 2) marked and a short note; every form is graded by the same scoring criteria;
• the coach's five-line report; and
• the conversation share link.

Submit in any accessible file type or as a link; a recorded response may be submitted as audio or video with a transcript, or as text.

Equivalent route (no AI required)

This route assesses the same Week 1 skills — pricing a choice by its opportunity cost, reading endpoints, slope, and points on a production possibilities frontier, and telling positive statements from normative ones — for comparable time and effort, about 60 to 90 minutes, the same as the coached route. Complete the same four problems, the four brief interpretations, and the message to the family member. Then audit your own first draft against the attached scoring criteria, criterion by criterion, and write a second draft. Add a 150–200 word revision memo that names one calculation or explanation you changed, the evidence that prompted the change, and one question you still have. Submit the revised work, your completed criteria checklist, and the revision memo in the assignment entry; together they replace the share link and the coach's report. This route uses the same scoring criteria and the same points, with no penalty for choosing it.

How you'll be graded

The full analytic rubric is attached to this assignment in Canvas.

Academic integrity and AI use

The calculations, reasoning, revision, and final report must be your own. Do not ask the chatbot to create the assignment or add evidence you did not produce, and do not let it tell you which side of a policy question is right. Submit an honest share link from your own dialogue. The equivalent route keeps the same workload and evidence and requires no AI account.

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