1. Supply & Demand: Elasticity & Applications
Chapter 4
Supply & Demand: Elasticity & Applications

2. Chapter Outline Price Elasticity of Demand & Supply
A.1. Price Elasticity of Demand
A.2. Elasticity & Revenue
A.3. Price Elasticity of Supply
Applications to Major Economic Issues
B.1 The Economics of Agriculture
B.2. Impact of a Tax on Price of Quantity
B.3. Minimum Floors & Maximum Ceilings

3. A- Price Elasticity of Demand & Supply
Supply & demand can often tell us whether certain forces increase or decrease quantities. But we need to know how much supply & demand respond to changes in price.
The quantitative relationship between price & quantity is analyzed using the crucial concept of elasticity.

4. A.1 Price elasticity of demand
“measures how much the quantity demanded of a good changes when its price changes” (the Sensitivity of QD to changes in Price) Or
“the percentage change in quantity demanded divided by the percentage change in price”
Elastic demand: means that the QD of the good responds greatly to changes in price
Inelastic demand: means that the QD of the good responds little to price changes

5. A.1 Price elasticity of demand (cont.)
Price elasticities tend to be higher when:
Price elasticities tend to be lower when???
The goods are luxuries
Substitutes are available
Consumers have more time to adjust their behavior

6. A.1 Price elasticity of demand (cont.)
Calculating Elasticities:
= ∆Q/Q ÷ ∆P/P
Or more precisely:
Where Q1 & P1 represent the original quantity & price, while Q2 & P2 stand for the new quantity & price.

7. A.1 Price elasticity of demand (cont.)
Categories of price elasticity
Price Elastic Demand
When 1% change in price causes more than 1% change in QD
Price Inelastic Demand
When 1% change in price causes less than 1% change in QD
Unit Elastic Demand
When % change in price causes exactly the same % change in QD

8. A.1 Price elasticity of demand (cont.)

9. A.1 Price elasticity of demand (cont.)
2 extreme cases of Elasticity:
Perfectly Inelastic demand
Ed = 0
Occurs when a change in price leads to no change at all in QD
The demand curve is a vertical curve
Perfectly Elastic demand
Ed = ∞
Occurs when a tiny change in price leads to an indefinitely large change in QD
The demand curve is a horizontal curve

10. A.1 Price elasticity of demand (cont.)
Example:
We drop the minus sign in the value of elasticity as it only reflects the inverse relationship between P &QD. We use the % change rather than absolute change which imply that the change in the units of measurements doesn’t affect the elasticity

11. A.1 Price elasticity of demand (cont.)

12. A.1 Price elasticity of demand (cont.)
A shortcut for calculating Elasticities:
The elasticity of a straight line at a point is given by the ratio of the length of the line segment below the point to the length of the line segment above the point.
“price elasticity is relatively large when we are up the linear DD curve & decreases as we go down the curve”
The elasticity at point B: the ratio of the line segment BZ to the segment AB equals 3:1 which means that the elasticity at this point is 3 (elastic).
The elasticity at point R: the ratio of the segment RZ to the segment AR is1/3 (inelastic)
Point M: unit elastic demand (ratio 2:2= 1)

13. A.1 Price elasticity of demand (cont.)

14. A.1 Price elasticity of demand (cont.)
The elasticity of a curved demand curve for a given point is given by drawing a line that is tangent to that point & then calculating the ratio of the segments for the tangent line.
The elasticity at point B in figure 4.5: the ratio of the line segment BZ to the segment AB equals 3:1 which means that the elasticity at this point is 3 (elastic).

15. A.1 Price elasticity of demand (cont.)
Elasticity is not the same as slope
The slope is not the same as the elasticity because the demand curve’s slope depends upon the changes in P & Q, whereas the elasticity depends upon the percentage changes in P & Q. The only exceptions are the polar cases of the completely elastic & inelastic demands.
Elasticities cannot be inferred by slope alone, it also depends on the specific price & quantity pair. The general rule is that the elasticity can be calculated as the ratio of the straight line or tangent segment below the demand point to the length of the segment above the point.

16. A.2. Elasticity & revenue
Many businesses want to know whether raising prices will raise or lower revenues. Let’s look at the relationship between price elasticity & total revenue.
Total Revenue (TR): is equal to price times quantity (P×Q). If consumers buy 5 units at $3 each, total revenue would be $15.
If you know the price elasticity of demand you will know what happen to TR when price changes:

17. A.2. Elasticity & revenue (cont.)

18. A.2. Elasticity & revenue (cont.)
An example:
A software company may have a wide range of different prices for their products in an attempt to exploit different elasticities.
If a consumer is desperate about buying a new operating system immediately, his elasticity would be low & the company will profit from charging a relatively high price.
On the other hand, if he is not in a hurry for an upgrade, his elasticity would be high & the company will profit from charging a relatively low price.
The paradox of the bumper harvest??

19. a.3. price elasticity of supply
“is the responsiveness of the quantity supplied of a good to changes in its market price.” OR
“The percentage change in quantity supplied divided by the percentage change in price.”
Cases of Elasticity of supply

20. a.3. price elasticity of supply (cont.)
As with demand elasticities, there are 2 extreme cases of supply elasticity (completely inelastic supply & completely elastic supply) between these extremes, we call supply elastic or inelastic depending on whether the % change in QS is larger (elastic) or smaller (inelastic) than or equal to (unit elastic) the % change in price.

21. a.3. price elasticity of supply (cont.)
What factors determine supply elasticity??
The ease with which production in the industry can be increased.
“If all inputs can be readily found at the going market prices, as is the case for the textile industry , then the output can be greatly increased with little increase in price. This would indicate that supply elasticity is relatively large. On the other hand, if production capacity is severely limited, as is the case for gold mining industry, then even large increases in the price of gold will call forth but a small response in supply. This would be inelastic supply.”

22. a.3. price elasticity of supply (cont.)
The time period under consideration.
“there’s a direct relationship between time & elasticity of supply. A change in price tends to have a larger effect on amount supplied as the time for suppliers to respond increases. But for very brief periods after a price increase, firms may be unable to increase their inputs of labor, materials, & capital, so supply may be price inelastic.”