Teach it. Check it. Revisit it.

Teacher guide

Audience: 13–18. Session: 45 minutes. Preparation: 10 minutes: open the free graph lab or prepare paper axes.

Prerequisites: Read graph axes and solve simple linear equations; adult guidance can support the algebra.

1. Spend 5 minutes asking learners to predict the result and explain their reasoning.
2. Use most of the session for the student activity. Ask learners to show calculations and name assumptions.
3. Reserve 5 minutes for the exit questions. Discuss why the answer follows, not just whether it matches.
4. Return to the follow-up next week without showing today’s answers first.

Student activity

Use demand P = 100 − Q and supply P = 20 + Q. Find equilibrium. Then model a drought by changing supply to P = 40 + Q. Predict the direction of change before calculating.

Write your prediction, calculation, explanation and one assumption you would check in a real situation.

Exit quiz

1. What are price and quantity before and after the drought?
2. Did demand fall when fewer units were purchased?

Teacher answers and reasoning

1. Initially Q = 40 and P = 60. After the shift Q = 30 and P = 70. Set the two equations equal to solve.
2. No. Supply shifted; the higher price reduced quantity demanded along the unchanged demand curve.

For each response, check the method, the result and the explanation. A correct number with an incorrect explanation needs another example.

Next-week review

Next week, restore the original curves and shift demand to P = 120 − Q. Predict, calculate Q = 50 and P = 70, and explain quantity supplied versus supply.

Facts, assumptions and policy debate

A graph describes outcomes under assumptions. Choosing a policy also requires considering distribution, fairness and effects omitted from the model.

Ask: what is calculated, what is assumed, and what is a judgment about priorities?