Price Elasticity of Demand Bell Ringer

Use this 12 minutes bell ringer to teach price elasticity of demand through one concrete decision. Students calculate midpoint elasticity and connect the coefficient to total revenue. Project the prompt before students enter. Give silent think time first, then require a written claim before discussion. The routine is short enough to repeat and specific enough to reveal who is reasoning and who is guessing.

The classroom prompt

A seller cuts price from $10 to $8 and sales rise from 100 to 140. Calculate price elasticity of demand with the midpoint method, classify demand, and decide whether total revenue rose or fell.

Put the question where every student can see it and do not supply vocabulary before students commit to an answer. Their first explanation becomes the evidence you use during the debrief.

Materials and setup

Display two observations: price falls from $10 to $8 and quantity demanded rises from 100 to 140 units.

Open the elasticity sandbox if you want students to test the same idea on an interactive model after the paper task. A projected version is enough; students do not need accounts for this lesson.

Run the lesson

Answer key and teacher moves

• Quantity changes by 40/120, or 33.33 percent.
• Price changes by 2/9, or 22.22 percent in absolute value.
• PED is 33.33/22.22 = 1.5, so demand is elastic.
• Total revenue rises from $1,000 to $1,120, consistent with an elastic-demand price cut.

Do not give credit for the correct direction alone. Ask students to name the changed determinant, identify the curve or quantity that changes, and connect the change to the final outcome. A complete explanation contains a cause, a model move, and a result.

What to collect

Collect one calculation with both midpoint denominators visible and a sentence connecting elasticity to revenue.

Most likely misconception: Students divide by the original value instead of the midpoint or keep the negative sign and classify negative 1.5 as inelastic.

Support and extension: Provide the midpoint formula but not the substituted numbers. Extend by asking for the revenue-maximizing implication near unit elasticity.

A clean closing question

End with: What changed, what stayed fixed, and what evidence proves your conclusion? That sentence works as the final written check because it forces students to separate a cause from the movement it produces. Collect it, scan for the misconception above, and use the first three minutes of the next class to repair the pattern if needed.

This resource is ready to copy into a slide, handout, or LMS assignment. If you assign it for points, publish the success criteria before students begin: correct model, correct direction, and an explanation that links the two.