Week 2 — Who Should Make the Sandwiches? A Short Trade Report

Assignment 2 of the term — work out who should make what at an illustrative food stand, prove that both partners gain from trading, and explain the result 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. Last week you learned that every choice has an opportunity cost; this week that idea decides who should make what. 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 question: who should make the sandwiches, and does anyone lose?

The task

You will use Dataset D, the campus food stand, an illustrative dataset constructed for this course (not real data). In one hour, Amara can make 8 smoothies or 4 sandwiches, and Diego can make 3 smoothies or 3 sandwiches. Each partner works 8 hours. Before trade, each splits the hours evenly, so Amara makes 32 smoothies and 16 sandwiches and Diego makes 12 smoothies and 12 sandwiches. Then Diego makes only sandwiches (24), Amara spends 6 hours on smoothies and 2 on sandwiches (48 smoothies and 8 sandwiches), and they trade at 1.5 smoothies per sandwich.

Work these four problems, showing your arithmetic and writing the units on every ratio:

1. At the illustrative campus food stand, Amara can make 8 smoothies or 4 sandwiches in one hour. What is her opportunity cost of making one sandwich, in smoothies per sandwich?
2. At the illustrative campus food stand, Amara can make 8 smoothies or 4 sandwiches in one hour. What is her opportunity cost of making one smoothie, in sandwiches per smoothie?
3. At the illustrative campus food stand, Diego trades 10 sandwiches to Amara at 1.5 smoothies per sandwich. How many smoothies does Diego receive?
4. At the illustrative campus food stand, Amara makes 16 sandwiches before trade; after specializing she makes 8 sandwiches and then receives 10 from Diego. How many more sandwiches does Amara have after the trade than before trade?

Beside each result, add one brief interpretation. For P1, say what the cost means and compare it with Diego's cost of 1 smoothie per sandwich to name who has the comparative advantage in sandwiches; keep that apart from who is faster. For P2, say how this cost relates to the P1 cost and compare it with Diego's cost of 1 sandwich per smoothie to name who has the comparative advantage in smoothies. For P3, check whether 1.5 lies between the two opportunity costs of a sandwich, and say why each partner accepts the rate. For P4, use the stand's totals, 44 smoothies and 28 sandwiches before trade and 48 and 32 after specializing, to explain how both partners can gain at once.

Explain it to a non-expert

A friend who runs a two-person bike-repair shop says, "I'm faster than my partner at both repairs and sales, so I should do everything myself." Write a 3–5 sentence message that answers your friend using what your results show, gives a reason tied to the food-stand data, and names one limit of the model — for example, that the numbers are illustrative, or that the model assumes each person's cost stays the same hour after hour. Explain any technical term, such as opportunity cost or comparative advantage, in everyday words. More than one way of putting it can be correct.

For a different, ungraded example, imagine two siblings splitting yard work, where the older one mows and rakes faster than the younger one. Model answer: "Being faster at both jobs doesn't mean you should do both. Every hour you spend raking is an hour of mowing you give up, and your sibling gives up less mowing for each bag raked. If you mow and your sibling rakes, the yard gets done sooner. This assumes neither of you gets tired, which real afternoons don't promise."

Use that pattern for the bike-repair shop, with your own results and reasoning.

Part 1 — Student instructions

1. Draft all four results, the four brief interpretations, and your message to the bike-shop friend 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. Reply 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 report for you.

Coach Prompt

COPY EVERYTHING BELOW THIS LINE
ROLE: You are a careful learning coach. Draw out and challenge MY thinking about opportunity cost, comparative advantage, the terms of trade, and the gains from trade. Do not write my assignment for me and do not invent work I did not show.

ASSIGNMENT: Work through these four problems in order, one at a time. Do not invent, replace, or reorder a problem. The data are illustrative, constructed for my course, not real: at the campus food stand, in one hour Amara can make 8 smoothies or 4 sandwiches and Diego can make 3 smoothies or 3 sandwiches; each works 8 hours; before trade Amara makes 32 smoothies and 16 sandwiches and Diego 12 and 12; after specializing Diego makes 24 sandwiches and Amara 48 smoothies and 8 sandwiches; they trade at 1.5 smoothies per sandwich. Do not supply any real-world figure, and never decree a verdict on trade policy.
PROBLEM P1: At the illustrative campus food stand, Amara can make 8 smoothies or 4 sandwiches in one hour. What is her opportunity cost of making one sandwich, in smoothies per sandwich?
PROBLEM P2: At the illustrative campus food stand, Amara can make 8 smoothies or 4 sandwiches in one hour. What is her opportunity cost of making one smoothie, in sandwiches per smoothie?
PROBLEM P3: At the illustrative campus food stand, Diego trades 10 sandwiches to Amara at 1.5 smoothies per sandwich. How many smoothies does Diego receive?
PROBLEM P4: At the illustrative campus food stand, Amara makes 16 sandwiches before trade; after specializing she makes 8 sandwiches and then receives 10 from Diego. How many more sandwiches does Amara have after the trade than before trade?
After the four results, I must briefly interpret each one: for P1, what the cost means, compared with Diego's cost of 1 smoothie per sandwich, to name who has the comparative advantage in sandwiches, kept apart from who is faster; for P2, how this cost relates to the P1 cost, compared with Diego's cost of 1 sandwich per smoothie, to name who has the comparative advantage in smoothies; for P3, whether 1.5 lies between the two opportunity costs of a sandwich and why each partner accepts it; for P4, how both partners gain at once, using the totals of 44 smoothies and 28 sandwiches before trade and 48 and 32 after specializing. I must then write a 3-5 sentence message to a friend who runs a two-person bike-repair shop and thinks the faster partner should do everything, with a reason tied to these data and one named limit of the model. I must explain technical terms in everyday words and write the units on every ratio.

SCORING CRITERIA: Score only evidence I supply: correct opportunity-cost and trade computations (40 points), reasoning about advantage and the gains from trade (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 opportunity cost, number of smoothies received, or gain in sandwiches, with its units = 2; the right values and operation with only an arithmetic slip = 1; a missing result or the wrong values or operation, such as an inverted ratio = 0. Do not penalize an alternative valid method or equivalent notation.
REASONING UNITS: For P1-P3 separately, an accurate account of what that value means plus its link to comparative advantage or the mutually beneficial range = 2; exactly one of the two = 1; neither = 0. Comparative advantage assigned by speed alone does not count. For P4, BOTH an accurate explanation of why both partners gain, using the before-and-after totals, AND a final message with a data-specific reason 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. An arithmetic slip alone is not a reasoning error.
CLARITY UNITS: For each problem, labeled evidence with units, understandable to someone new to economics, with technical terms explained = 2; intelligible evidence that needs rereading because of ambiguity, missing units, 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, units, 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 reply. 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 reply 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 results and their brief interpretations AND written my message to the bike-shop friend 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 trade report, and the share link.
COPY EVERYTHING ABOVE THIS LINE

Deliverables

Submit these three items in the assignment entry:

• your revised trade report with all four results, their brief interpretations, and your message to the bike-shop friend — written, or recorded as audio or video with a transcript, or as a labelled spreadsheet with 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 2 skills — building opportunity costs one ratio at a time with their units, naming comparative advantage by the lower cost, checking the terms of trade against the mutually beneficial range, and proving the gains from trade — 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 bike-shop friend. 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 trade report, 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. Submit an honest share link from your own dialogue. The equivalent route keeps the same workload and evidence and requires no AI account.

Built with The Course Maker · samples.thecoursemaker.com