## Elasticity: A Measure of Response

Read this chapter to learn about the concept of elasticity. Be sure to read Sections 5.1-5.4 following the introduction.

### The Price Elasticity of Demand

#### Answer to Try It Problem

- The absolute value of price elasticity of demand tends to be greater when more time is allowed for consumers to respond. Over time, riders of the commuter rail system can organize car pools, move, or otherwise adjust to the fare increase.
- Using the formula for price elasticity of demand and plugging in values for the estimate of price elasticity (−0.5) and the percentage change in price (5%) and then rearranging terms, we can solve for the percentage change in quantity demanded
as:
*e*_{D}= %Δ in*Q*/%Δ in*P*; −0.5 = %Δ in*Q*/5%; (−0.5)(5%) = %Δ in*Q*= −2.5%. Ridership falls by 2.5% in the first few months. - Using the formula for price elasticity of demand and plugging in values for the estimate of price elasticity over a few years (−1.5) and the percentage change in price (5%), we can solve for the percentage change in quantity demanded as
*e*_{D}= %Δ in*Q*/%Δ in*P*; −1.5 = %Δ in*Q*/5%; (−1.5)(5%) = %Δ in*Q*= −7.5%. Ridership falls by 7.5% over a few years. - Total revenue rises immediately after the fare increase, since demand over the immediate period is price inelastic. Total revenue falls after a few years, since demand changes and becomes price elastic.