Week 4 — Assignment (Adaptive Learning) · Supply, Equilibrium & Comparative Statics Problem Set

Course: Principles of Microeconomics (ECON 1) · Silver Oak University (fictional sample) · Prof. Kessler
Objective 2 · SLO A & B · Assignment 4 of 14 · 100 points
This is the configured (adaptive) variant. An AI coach gives you the problems one at a time, grades each against an embedded rubric, lets you retry a fresh version, and produces a self-scored report. You submit the report (first line STUDENT'S SCORE: X/100) + your chat share link. (The traditional, instructor-graded version is in I-assignment-and-rubric-week-04-traditional.md.)

How to run this

1. Open an approved chatbot (Gemini, Claude, ChatGPT). Copy the whole gray box and paste it as one message.
2. Solve each problem; the coach grades it, teaches the gaps, and offers a fresh variant to raise your score.
3. When you get the report, submit it (it starts with STUDENT'S SCORE: X/100) plus your chat share link in Canvas. Due Sun, Sep 27.

You are my assignment coach and grader for Week 4 of Principles of Microeconomics (ECON 1)
at Silver Oak University. Give me the problems below ONE AT A TIME, let me solve each, grade
my answer against the rubric, show me how to improve, and let me re-try a fresh version to
raise my score. Grade ONLY against the answer key and rubric below — never invent problems,
answers, or scores. Redo any arithmetic yourself and SHOW YOUR WORK before telling me I'm
wrong. Score honestly; a wrong answer scores low, a strong answer earns full marks.

START: greet me in 1–2 sentences, ask my FIRST NAME, then give Problem 1 exactly as written.
If I answer without giving my name, keep going but ask before the final report. ONE problem
at a time; never show the whole set, the answers, the variants, or the rubric. After each
answer: grade it, say what I did well, TEACH the gap, then offer a re-attempt on the FRESH
VARIANT (update my score to my BEST attempt, capped at full marks). Judge meaning, not
wording. Every message ends with a problem, a question, or a next step.

================= PROBLEM 1 (25 pts) — Solve for equilibrium =================
PROBLEM: "A market has demand Qd = 120 − 3P and supply Qs = −30 + 3P. (a) Find the
equilibrium price P* and equilibrium quantity Q*. Show every algebra step. (b) Verify your
answer by plugging P* into BOTH equations and confirming they give the same Q."
VETTED ANSWER: Set equal: 120 − 3P = −30 + 3P → 150 = 6P → P* = 25. Q* = 120 − 3·25 =
120 − 75 = 45. Check: Qs = −30 + 3·25 = −30 + 75 = 45. ✓ Equilibrium: P* = $25, Q* = 45 units.
RUBRIC: 25 = correct P* and Q* with every algebra step shown AND the verification check. 
15–20 = correct P* and Q* but check step missing or arithmetic slip in Q*. 8–14 = method
right (set Qd = Qs), one algebra error. 0–7 = wrong method (e.g., adds equations instead
of equating them).
FRESH VARIANT: "Qd = 90 − 2P, Qs = −30 + 4P. Find P* and Q*; verify."
ANSWER: 90 − 2P = −30 + 4P → 120 = 6P → P* = 20. Q* = 90 − 40 = 50. Check: Qs = −30 + 80 = 50. ✓

================= PROBLEM 2 (25 pts) — Surplus/shortage at a stated price =================
PROBLEM: "Using the same market (Qd = 120 − 3P, Qs = −30 + 3P, P* = $25, Q* = 45): at a
price of P = $15, what is the quantity demanded, the quantity supplied, and the size and
TYPE (surplus or shortage) of the market imbalance? Explain what price pressure results."
VETTED ANSWER: At P = 15: Qd = 120 − 45 = 75; Qs = −30 + 45 = 15. Qd > Qs → SHORTAGE of
75 − 15 = 60 units. Because quantity demanded (75) exceeds quantity supplied (15), buyers
compete for scarce units → sellers raise price → price RISES toward equilibrium ($25).
RUBRIC: 25 = correct Qd=75, Qs=15, shortage=60 with arithmetic shown, AND the price-pressure
direction stated in words. 15–20 = numbers right, direction or interpretation thin. 8–14 =
one number wrong or calls it a "surplus" instead of shortage. 0–7 = no meaningful attempt.
FRESH VARIANT: "Same market (Qd = 120 − 3P, Qs = −30 + 3P, P* = $25): at P = $35, find Qd,
Qs, the imbalance size and type, and the price pressure."
ANSWER: Qd = 120 − 105 = 15; Qs = −30 + 105 = 75. SURPLUS of 75 − 15 = 60. Qs > Qd →
unsold goods pile up → sellers cut price → price FALLS toward $25.

================= PROBLEM 3 (25 pts) — Comparative statics: a supply shock =================
PROBLEM: "Still using Qd = 120 − 3P. Now suppose a new technology reduces production costs,
increasing supply by 24 units at every price (so the new supply is Qs_new = −30 + 3P + 24
= −6 + 3P). (a) Describe what happened to the supply curve (which direction did it shift,
and why?). (b) Find the new equilibrium P and Q. (c) Compare the new P and Q to the
original P* = $25, Q* = 45 — did P rise or fall? Did Q rise or fall? Does this match the
direction rule for a supply increase?"
VETTED ANSWER: (a) Supply increased → supply curve shifted RIGHT (more Q at every P). Better
technology lowers production costs, making producers willing to supply more at each price.
(b) New equilibrium: 120 − 3P = −6 + 3P → 126 = 6P → New P = 21. New Q = 120 − 63 = 57.
Check: Qs_new = −6 + 63 = 57. ✓ (c) P fell from $25 to $21 (P DOWN ✓). Q rose from 45 to
57 (Q UP ✓). Matches the direction rule: ↑ Supply → P↓, Q↑. ✓
RUBRIC: 25 = correct shift direction identified (right) with reason given (tech lowers cost);
correct new P=21 and Q=57 with algebra shown; direction confirmed and direction rule stated.
15–20 = numbers right, shift direction or rule interpretation thin. 8–14 = shift identified
correctly but algebra error. 0–7 = wrong direction or says price rises when supply increases.
FRESH VARIANT: "Same original market (Qd = 120 − 3P, P* = $25, Q* = 45). Now suppose input
costs rise, DECREASING supply by 24 units (Qs_new = −30 + 3P − 24 = −54 + 3P). Describe
the shift, find the new equilibrium, and confirm the direction rule."
ANSWER: Supply decreases → curve shifts LEFT. New eq: 120 − 3P = −54 + 3P → 174 = 6P →
New P = 29. New Q = 120 − 87 = 33. Check: −54 + 87 = 33. ✓ P rose ($25 → $29) ✓; Q fell
(45 → 33) ✓. ↓ Supply → P↑, Q↓. ✓

================= PROBLEM 4 (25 pts) — Applied supply reasoning =================
PROBLEM: "A city experiences two simultaneous changes in its apartment rental market: (i)
construction costs fall sharply (cheaper materials), AND (ii) the city's population rises
(more renters move in). (a) For each change, identify which curve shifts (demand or supply)
and in which direction. (b) What can you say with confidence about the new equilibrium
quantity of apartments rented? (c) What can you say about the new equilibrium rent (price)?
Label any claim that is ambiguous as 'indeterminate' and explain why."
VETTED ANSWER: (a) Cheaper construction costs → supply of apartments INCREASES → supply
curve shifts RIGHT. Population rises → more renters → demand for apartments INCREASES →
demand curve shifts RIGHT. (b) Both shifts increase equilibrium quantity. Q is unambiguously
HIGHER than before (both ↑Supply and ↑Demand push Q up). (c) Supply increase pushes rent
DOWN; demand increase pushes rent UP. These forces work in opposite directions. Without
knowing which shift is larger, the change in rent (P) is INDETERMINATE (ambiguous). A city
where supply rises a lot may see rents fall even as population grows; one where demand
outpaces supply will see rents rise.
RUBRIC: 25 = both shifts correctly identified (supply right, demand right) with reason; Q
stated as unambiguously higher; P correctly labeled indeterminate with explanation of the
opposing forces. 15–20 = shifts right, Q right, but P not identified as indeterminate (says
P rises or falls without acknowledging the ambiguity). 8–14 = one shift wrong or P analysis
missing. 0–7 = mostly wrong.
FRESH VARIANT: "A coffee market: the price of coffee beans (an input) falls AND income in
the area rises (coffee is a normal good). (a) Which curves shift and which way? (b) Is the
new equilibrium quantity of coffee indeterminate or determinate? (c) Is the new price
indeterminate or determinate?"
ANSWER: (a) Lower input cost → supply increases (right). Higher income + normal good →
demand increases (right). (b) Q is unambiguously HIGHER (both curves push Q up — determinate).
(c) P is INDETERMINATE (supply pushes P down, demand pushes P up; need magnitudes to tell).

================= COMPLETION =================
After all four problems (and any re-attempts), produce EXACTLY:
    STUDENT'S SCORE: X/100
    WEEK 4 ASSIGNMENT — Supply, Equilibrium & Comparative Statics
    Student: [name] | Date: ___
    Problem 1: a/25 — [one-line note]
    Problem 2: b/25 — [one-line note]
    Problem 3: c/25 — [one-line note]
    Problem 4: d/25 — [one-line note]
    Strongest skill: ___
    Worth another look: ___
Then say, verbatim: "Copy this entire report AND your share link to this chat, and submit both
in Canvas for this assignment." End with one genuine sentence of encouragement.

Instructor grading note + rubric (for Canvas)

Record the AI score (line 1); spot-check a sample against the chat share link. The embedded key makes scores consistent across chatbots. Summary rubric (each problem to 25, total 100):

Quality gate (self-checked): P1: 150/6=25, Q*=45, check Qs=45 ✓; P2: Qd=75, Qs=15, shortage=60 ✓; P3: 126/6=21, Q=57, check 57 ✓, direction P↓ Q↑ confirmed ✓; P4: two rightward shifts, Q up (determinate), P indeterminate (correct) ✓; variants all Python-verified ✓; every curve-shift direction cross-checked against discipline reference ✓.

Canvas placement block

canvas_object    = Assignment
title            = "Week 4 Assignment — Supply, Equilibrium & Comparative Statics (adaptive)"
assignment_group = "Assignments"
points_possible  = 100
grading_type     = points
submission_types = [online_text_entry, online_url]
due_offset_days  = 6
published        = true
submission_note  = "Paste the AI summary report (score on line 1) + the chat share link."
provenance       = "~ Prof. Kessler's edition · Fall 2026 · built with thecoursemaker.com"

Traditional variant — for comparison. This course is configured adaptive learning, so the actual Week-4 assignment is the AI-coached version in I-assignment-and-rubric-week-04.md. This file shows the same problem set built the traditional way — students complete it and submit; the instructor grades against the rubric. (Choosing assignment_type = traditional at setup generates this style.)

Course: Principles of Microeconomics (ECON 1) · Silver Oak University (fictional sample) · Prof. Kessler
Objective 2 · SLO A & B · Assignment 4 of 14 · 100 points · Due Sun, Sep 27

The Assignment

Show your work and write your interpretations in complete sentences. Submit as a document or text entry.

Problem 1 — Solve for equilibrium (25 pts). A market has demand Qd = 120 − 3P and supply Qs = −30 + 3P.
(a) Find the equilibrium price P* and equilibrium quantity Q*. Show every algebra step.
(b) Verify your answer by plugging P* into BOTH equations and confirming they give the same Q.

Problem 2 — Surplus/shortage at a stated price (25 pts). Using the same market (Qd = 120 − 3P, Qs = −30 + 3P, P* = $25):
At a price of P = $15, compute the quantity demanded, the quantity supplied, and the size and type (surplus or shortage) of the market imbalance. In one sentence, explain what price pressure results and why.

Problem 3 — Comparative statics: a supply shock (25 pts). Still using Qd = 120 − 3P. A new technology reduces production costs, increasing supply by 24 units at every price, so the new supply is Qs_new = −6 + 3P.
(a) Describe what happened to the supply curve — which direction did it shift, and why?
(b) Find the new equilibrium price and quantity (show the algebra).
(c) Compare the new P and Q to the original P* = $25, Q* = 45. Did price rise or fall? Did quantity rise or fall? Does this match the direction rule for a supply increase?

Problem 4 — Applied supply reasoning (25 pts). A city's apartment rental market experiences two simultaneous changes: (i) construction costs fall sharply, and (ii) the city's population rises (more people want to rent).
(a) For each change, identify which curve shifts (demand or supply) and in which direction.
(b) What can you say with confidence about the new equilibrium quantity of apartments rented?
(c) What can you say about the new equilibrium rent (price)? Label any claim that is ambiguous as "indeterminate" and explain why.

AI note. This is the traditional format — submit your own work. You may use an approved chatbot to check an algebra step or look up a supply-and-demand concept, but add a one-line note of which tool and how. (In the adaptive version, working the problems with the chatbot is the activity.)

Grading rubric — 100 points

Instructor answer key & worked solutions — REMOVE BEFORE PUBLISHING TO STUDENTS

P1: Set Qd = Qs: 120 − 3P = −30 + 3P → 150 = 6P → P* = $25. Q* = 120 − 75 = 45. Check: Qs = −30 + 75 = 45. ✓ (Numbers Python-verified.)

P2: At P = 15: Qd = 120 − 45 = 75; Qs = −30 + 45 = 15. Qd > Qs → SHORTAGE of 60 units. Buyers compete → sellers raise price → price RISES toward equilibrium. (Verified.)

P3: (a) Technology lowers cost → supply increases → curve shifts RIGHT (more Q at every P). (b) New eq: 120 − 3P = −6 + 3P → 126 = 6P → New P = $21. New Q = 120 − 63 = 57. Check: −6 + 63 = 57 ✓. (c) P fell ($25 → $21, DOWN ✓); Q rose (45 → 57, UP ✓). Matches ↑ Supply → P↓, Q↑ ✓. (All values Python-verified.)

P4: (a) Lower construction cost → supply increases (rightward shift). Population rise → more renters → demand increases (rightward shift). (b) Both shifts push Q up → Q is unambiguously HIGHER (determinate). (c) Supply increase pushes P down; demand increase pushes P up — opposite forces. Without knowing which is larger, P is INDETERMINATE (ambiguous). Full-credit answer explains the opposing forces explicitly.

Quality gate (self-checked): P1 150/6=25, Q=45 ✓; P2 Qd=75, Qs=15, shortage=60 ✓; P3 126/6=21, Q=57, check 57 ✓, direction ↑Supply → P↓,Q↑ ✓; P4 both shifts right, Q determinate up, P indeterminate ✓; all curve-shift directions cross-checked against discipline reference ✓.

Canvas placement block

canvas_object    = Assignment
title            = "Week 4 Assignment — Supply, Equilibrium & Comparative Statics (traditional)"
assignment_group = "Assignments"
points_possible  = 100
grading_type     = points
submission_types = [online_upload, online_text_entry]
due_offset_days  = 6
rubric_ref       = "w04-assignment-rubric"
published        = true
provenance       = "~ Prof. Kessler's edition · Fall 2026 · built with thecoursemaker.com"