Price Elasticity of Demand and Supply Study Pack

Kibin's free study pack on Price Elasticity of Demand and Supply includes a 4-section study guide, 8 quiz questions, 10 flashcards, and 1 open-ended Explain review question. Sign up free to track your progress toward mastery, plus upload your own notes and recordings to create personalized study packs organized by course.

Last updated May 21, 2026

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Price Elasticity of Demand and Supply Study Guide

Master the mechanics of price elasticity by working through both demand and supply responsiveness, elastic versus inelastic classifications, and the midpoint method for accurate calculations. This pack covers key determinants like substitutes, necessity versus luxury status, and time horizons, then connects elasticity directly to tax burden distribution and the often-surprising relationship between price changes and total revenue.

Key Takeaways

  • •Price elasticity of demand measures how sensitive the quantity demanded of a good is to a change in its price, calculated as the percentage change in quantity demanded divided by the percentage change in price.
  • •Demand is elastic when the absolute value of elasticity exceeds 1 (consumers respond strongly to price changes), inelastic when it is less than 1 (consumers respond weakly), and unit elastic when it equals exactly 1.
  • •Key determinants of demand elasticity include the availability of substitutes, whether the good is a necessity or luxury, the share of income the good consumes, and the time horizon consumers have to adjust.
  • •Price elasticity of supply measures how responsive producers are to price changes, using the same ratio structure; supply tends to be more elastic over longer time horizons because producers have more opportunities to adjust inputs and capacity.
  • •The midpoint method calculates elasticity using the average of two prices and two quantities as the denominator, preventing different elasticity values from being generated depending on the direction of the price change.
  • •Elasticity determines how tax burdens are shared between buyers and sellers, and explains the relationship between price changes and total revenue — a counterintuitive result where raising prices can decrease a firm's revenue if demand is elastic.

The Core Concept: What Elasticity Measures

Elasticity is a standardized way to quantify responsiveness — specifically, how much one variable changes in percentage terms when another variable changes by one percent. In the context of markets, price elasticity focuses on how buyers and sellers react when the price of a good shifts.

Why Percentages Instead of Absolute Numbers

  • •Comparing raw unit changes across goods is meaningless — a one-dollar price change matters very differently for a pack of gum versus a car.
  • •Using percentage changes creates a unit-free ratio that allows consistent comparison across any good or market.

The Elasticity Formula

  • •Price elasticity of demand = (% change in quantity demanded) ÷ (% change in price).
  • •Because demand curves slope downward, this ratio is inherently negative; economists typically work with the absolute value to simplify interpretation.
  • •Price elasticity of supply = (% change in quantity supplied) ÷ (% change in price), which yields a positive value since supply curves slope upward.

Calculating Elasticity Accurately: The Midpoint Method

A straightforward percentage calculation produces different elasticity values depending on whether price is rising or falling, which creates inconsistency. The midpoint method resolves this by anchoring both percentage changes to the average of the two endpoints.

Midpoint Method Formula

  • •% change in quantity = (Q2 − Q1) ÷ [(Q1 + Q2) ÷ 2] × 100.
  • •% change in price = (P2 − P1) ÷ [(P1 + P2) ÷ 2] × 100.
  • •Dividing the resulting percentage changes yields the same elasticity value regardless of whether price increases or decreases between the two points.

Worked Example Logic

  • •If price rises from $8 to $10 and quantity demanded falls from 120 to 80 units, the midpoint price is $9 and the midpoint quantity is 100.
  • •The percentage change in quantity is −40%, the percentage change in price is +22.2%, giving an elasticity of approximately −1.8 (elastic demand).

About this Study Pack

Created by Kibin to help students review key concepts, prepare for exams, and study more effectively. This Study Pack was checked for accuracy and curriculum alignment using authoritative educational sources. See sources below.

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