# ECO101H1 Lecture Notes - Lecture 6: Tennis Ball, Toronto Transit Commission, Demand Curve

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1 Aug 2010
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Thursday, October 1st, 2009.
Elasticity of Demand
Insight: If the choice is between A or B, you need information about A and B.
If you have decided on A, information about B (only) is required to identify the
opportunity cost of A if B is the next best alternative to A.
Total Revenue Ā± Price x Quantity
Questions:
1) If Toronto Transit commission wished to increase Total Revenue, should it
increase price (fare)?
2) You own one of the 5 toll bridges across a river, each of which sets the price (toll)
at \$5.00.
If you wish to increase Total Revenue, should you increase price (toll)?
Fare increase: (1) For those who continue to ride the TTC, fares will be higher,
BUT
(2) There will be fewer riders (per the law of downward-sloping
demand)
Result: Law of downward-sloping demand is not sufficient to answer question.
(Price) Elasticity of Demand
Definition: Percent change in quantity demanded /
Percent change in price
% ĀØ4D
īīĀØ3ī (Ignore minus sign)
Measures responsiveness of quantity demanded to a change in price.
Mid-point Convention
īīĀØ4 = ĀØ4
Q (Q = Average quantity)
īīĀØ3ī ĀØī3
P (P = average price)
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Example:
Situation Price Quantity Demanded
A 0.90 1100
B 1.10 900
īīĀØī4XDQWLW\ī'HPDQGHGī = 200 x 100
(1100 + 900)/2
= 200 x 100
1000
= 20%
īīĀØī3ULFH = 0.2 x 100
(0.9 + 1.10)/2
= 0.20 x 100
1.00
= 20%
ELASTICITY = 20% = 1.0
20%
Insight: same result if go up demand curve from A to B or down demand curve
from B to A!
Terminology:
perfectly inelastic: elasticity = 0
inelastic: 0 < elasticity < 1
unit elastic: elasticity = 1
elastic: 1 < elasticity < ī
perfectly elasticīīīHODVWLFLW\ī īī
#1 % ĀØ3īīī īīī
īīĀØ4D = 20 elasticity = 20 / 10 = 2
Ć Quantity demanded is very responsive to a change in price
#2 % ĀØ3īīī īīī
īīĀØ4D = 2 elasticity = 2 / 10 = 0.2
Ć Quantity demanded is not very responsive to a change in price
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