Today Price elasticity of demand Chapter 18 Elasticity

Today Price elasticity of demand

Chapter 18 Elasticity

How does a Change in Supply Affect Price & Quantity? Want a quantitative answer. Suppose new safety regulations increase the cost of producing toasters. How much does price increase? How much does quantity decrease?

How much do P & Q change? P S’ S Depends on: shape of D curve P where you are on the D curve. D Q Q

Price Elasticity of Demand How responsive the quantity demanded is to changes in price.

Availability of Substitutes The more and better the substitutes, the higher the price elasticity, since as the price rises consumers switch to other products easily. Note: the more broadly one defines a good, the lower the elasticity. Ex: citrus fruits v. fresh produce Ex: toothpaste v. Aim toothpaste

Proportion of Income Spent on the Good The higher the proportion, the higher the price elasticity. Ex: salt v. housing

Price Elasticity of Demand: Formula % QD = QD/ave. Q % P P/ave. P QD/ave. Q = Q 0 -Q 1 (Q 0+Q 1)/2 P/ave. P= P 0 -P 1 (P 0+P 1)/2

An Example P S’ % QD =(7 -3) (100) (7+3)/2 % P =(5 -7) (100) (5+7)/2 D =4/5 -2/6 = -2. 4 Q S 7 5 3 7

Interpreting the Answer Negative sign: The price elasticity of D will always have a negative sign. (Why? ) By convention, we usually drop the negative sign & focus on the absolute value of . Note: sign is still imp’t for other elasticities we’ll study later.

Interpreting the Magnitude = % QD/ % P = 2. 4 The quantity demanded will fall by 2. 4 % for every 1% increase in price. Ex: If price rises 15%, then QD will fall by 36%.

Elastic Demand We say that demand is elastic when > 1. % Q D> % P Total revenue (P x Q) moves in the same direction as QD. If price rises, QD falls by a larger %, total revenue falls. If price falls, QD rises by a larger %, total revenue rises.

Unit Elastic We say that demand is unit elastic when = 1. % QD = % P Total revenue (P x Q) unchanged as price changes.

Inelastic We say that demand is inelastic when < 1. % QD< % P Total revenue (P x Q) moves in the same direction as price. If price rises, QD falls by a smaller %, total revenue rises. If price falls, QD rises by a smaller %, total revenue falls.

Relating Elasticity to the Shape of & Location on D curve P >1 =1 <1 D Q Straight-line demand curve: Elasticity falls as you move down the D curve. See textbook for a numerical example.

Revenue Maximization & Straight-Line Demand P >1 = 1, unit <1 D Q When elastic, what happens to revenue as price falls? When inelastic, what happen to revenue as price falls? Where is revenue maximized?

Revenue Max. & Profit Max. Are they the same thing?

Perfectly Inelastic Demand P D = %QD/ % P =0 (Violates the Law of Demand) Q

Perfectly Elastic Demand P D Q = % QD/ % P = Violates the Law of Demand

Comparing 2 straight-line D curves P pt. C DA Begin at pt. C. Same P change. Change in Q very different DB Q

Comparing 2 straight-line D curves DA is steeper, less elastic (more inelastic) compared to DB at the point where they cross.

Short Run versus Long Run Short run (SR): the period after some change, but before adjustments to the change are complete. Long run (LR): the period after some change, once all adjustments to the change have been made.

Elasticity in the SR & LR Short Run Quantity demanded has a limited response to changes in price. Demand is less elastic Long Run response to changes in price is complete. Demand is more elastic.

Demand in the LR and SR P pt. A pt. B DSR DLR represents complete adjustment to new P. DSR shows initial response to P, given initial P. pt. C DSR Q DLR

Coming Up Other demand elasticities. Price elasticity of supply.

Group Work Problems relating to price elasticity of demand. work 1 &3 first, even-numbered groups work 2 & 4 first.

1. Sale of Fresh Green Beans Calculate the price elasticity of demand using the data above. Show your work. Is the demand for green beans price elastic, unit elastic, or price inelastic?

2. Price Elasticity Suppose that = 1. 25 and price falls from $7. 00 to $5. 00. By what percentage will the quantity demanded increase? Show your work. Will revenue rise or fall as a result? How do you know?

3. Pricing parking spaces in a parking lot You think that if you reduce prices then you will be able to fill more spots and therefore earn more money. Your friend says that you should raise prices and thereby increase revenue even if fewer people park there. Suppose you find out that the elasticity of demand (at your current price) is equal to 0. 80. How can this information settle your debate?