Chapter 19
Theory of Consumer Behavior
Copyright 2002 by The McGrawHill Companies, Inc. All rights reserved.
191
Chapter Objectives
•
•
•
•
•
•
Marginal utility
The law of diminishing returns
Total utility
Maximizing utility
The waterdiamond paradox
Consumer surplus
Copyright 2002 by The McGrawHill Companies, Inc. All rights reserved.
192
Utility
• What is utility?
– Utility is NOT usefulness!
– Utility means only that you think enough of
something to buy it
– Utility is measured by how much you are
willing to pay for something
Copyright 2002 by The McGrawHill Companies, Inc. All rights reserved.
193
Hypothetical Demand Schedule
for Hamburgers
Price
Units
Purchased
$2.75
1
Copyright 2002 by The McGrawHill Companies, Inc. All rights reserved.
194
Hypothetical Demand Schedule
for Hamburgers
Price
Units
Purchased
$2.75
1
2.00
2
Copyright 2002 by The McGrawHill Companies, Inc. All rights reserved.
195
Hypothetical Demand Schedule
for Hamburgers
Price
Units
Purchased
$2.75
1
2.00
2
1.00
3
Copyright 2002 by The McGrawHill Companies, Inc. All rights reserved.
196
Hypothetical Demand Schedule
for Hamburgers
Price
Units
Purchased
$2.75
1
2.00
2
1.00
3
.25
4
Copyright 2002 by The McGrawHill Companies, Inc. All rights reserved.
197
Marginal Utility is the additional utility derived
from consuming one more unit of a good or service
Price
Units
Purchased MU
$2.75
1
$2.75
2.00
2
2.00
1.00
3
1.00
.25
4
.25
Copyright 2002 by The McGrawHill Companies, Inc. All rights reserved.
198
Marginal Utility is the additional utility derived
from consuming one more unit of a good or service
Price
Purchased MU
$2.75
1
$2.75
2.00
2
2.00
1.00
3
1.00
.25
4
.25
Note: Marginal Utility is the
same as the price.
Copyright 2002 by The McGrawHill Companies, Inc. All rights reserved.
199
Law of Diminishing Marginal Utility: As we consume more
and more of a good or service,we like it less and less
Price
Units
Purchased MU
$2.75
1
$2.75
2.00
2
2.00
1.00
3
1.00
.25
4
.25
Copyright 2002 by The McGrawHill Companies, Inc. All rights reserved.
1910
Total Utility is the utility derived from consuming
a certain number of units of a good or service
Price
Units
Purchased MU
$2.75
1
$2.75 $2.75
2.00
2
2.00
1.00
3
1.00
.25
4
.25
Copyright 2002 by The McGrawHill Companies, Inc. All rights reserved.
TU
1911
Total Utility is the utility derived from consuming
a certain number of units of a good or service
Price
Units
Purchased MU
$2.75
1
2.00
2
2.00
1.00
3
1.00
.25
4
.25
TU
$2.75 $2.75
Copyright 2002 by The McGrawHill Companies, Inc. All rights reserved.
4.75
1912
Total Utility is the utility derived from consuming
a certain number of units of a good or service
Price
Units
Purchased MU
$2.75
1
2.00
2
1.00
3
.25
4 .25
TU
$2.75 $2.75
2.00
4.75
1.00
5.75
Copyright 2002 by The McGrawHill Companies, Inc. All rights reserved.
1913
Total Utility is the utility derived from consuming
a certain number of units of a good or service
Price
Units
Purchased MU
$2.75
1
2.00
2
1.00
3
.25
4 .25 6.00
TU
$2.75 $2.75
2.00
4.75
1.00
5.75
Copyright 2002 by The McGrawHill Companies, Inc. All rights reserved.
1914
Total Utility is the utility derived from consuming
a certain number of units of a good or service
Units
Price Purchased MU
$2.75 1
TU
$2.75 $2.75
2.00 2
2.00 4.75
1.00 3
1.00
5.75
.25 4
.25
6.00
To get total utility, just add up the marginal utilities of
the units purchased
Copyright 2002 by The McGrawHill Companies, Inc. All rights reserved.
1915
Maximizing Utility
• How much we buy of any good or service
depends on
– Its price
– Our marginal utility schedule
Price
Units
Purchased
MU
$2.75
1
$2.75 $2.75
2.00
2
2.00 4.75
1.00
3
1.00 5.75
.25
4
.25 6.00
TU
In real life there is usually only ONE price!
Copyright 2002 by The McGrawHill Companies, Inc. All rights reserved.
1916
Maximizing Utility
• We try to spend our money on what will give us
the most utility!
– As we consume more of a good or service, its utility
declines!
– This means that we will keep buying more of a good
or service until our marginal utility falls to the
level of the price. At this point marginal
utility is the same as the price.
Copyright 2002 by The McGrawHill Companies, Inc. All rights reserved.
1917
Maximizing Utility
• We try to spend our money on what will give us
the most utility!
– As we consume more of a good or service, its utility
declines!
– This means that we will keep buying more of a good
or service until our marginal utility falls to the
level of the price. At this point marginal
utility is the same as the price.
Marginal Utility
Price
= 1
Copyright 2002 by The McGrawHill Companies, Inc. All rights reserved.
1918
Maximizing Utility
• We try to spend our money on what will give us
the most utility!
– Remember, as we consume more of a good or
service, its utility declines!
– This means that we will keep buying more of a good
or service until our MU falls to the level of the
price
The price is $1.00. How many units would you buy?
Price
Units
Purchased
MU
$2.75
1
$2.75 $2.75
2.00
2
2.00 4.75
1.00
3
1.00 5.75
.25
4
.25 6.00
Copyright 2002 by The McGrawHill Companies, Inc. All rights reserved.
TU
The answer is 3
1919
Maximizing Utility
• We try to spend our money on what will give us
the most utility!
– Remember, as we consume more of a good or
service, its utility declines!
– This means that we will keep buying more of a good
or service until our MU falls to the level of the
price
The MU of the last unit purchased will always equal its price
Price
Units
Purchased
MU
$2.75
1
$2.75 $2.75
2.00
2
2.00 4.75
1.00
3
1.00 5.75
.25
4
.25 6.00
Copyright 2002 by The McGrawHill Companies, Inc. All rights reserved.
TU
The answer is 3
1920
Maximizing Utility
• We try to spend our money on what will give us
the most utility!
– Remember, as we consume more of a good or
service, its utility declines!
– This means that we will keep buying more of a good
or service until our MU falls to the level of the
price
The price is $2. How many units will you buy?
Price
Units
Purchased
MU
$2.75
1
$2.75 $2.75
2.00
2
2.00 4.75
1.00
3
1.00 5.75
.25
4
.25 6.00
Copyright 2002 by The McGrawHill Companies, Inc. All rights reserved.
TU
The answer is 2
1921
Maximizing Utility
• We try to spend our money on what will give us
the most utility!
– Remember, as we consume more of a good or
service, its utility declines!
– This means that we will keep buying more of a good
or service until our MU falls to the level of the
price The MU of the last unit purchased will always equal its price
Price
Units
Purchased
MU
$2.75
1
$2.75 $2.75
2.00
2
2.00 4.75
1.00
3
1.00 5.75
.25
4
.25 6.00
Copyright 2002 by The McGrawHill Companies, Inc. All rights reserved.
TU
The answer is 2
1922
General Utility Formula
• The MU of the last unit purchased will
always equal its price
MU 2.75 2.00 1.00 .25
=
=
=
= .25 = 1
1.00
Price
2.75
2.00
If this is true for hamburgers it will be true for everything else
MU1 MU2 MU3 MUn
=
=
=
Pn
P3
P2
P1
Remember, we will keep buying anything until its MU
declines to the price level
Copyright 2002 by The McGrawHill Companies, Inc. All rights reserved.
1923
Price
Purchased
MU
TU
$2.75
1
$2.75 $2.75
2.00
2
2.00 4.75
1.00
3
1.00 5.75
.25
4
.25 6.00
0 0 0 6.00
If a good or service were free, you would keep consuming
until the MU fell to zero
As we consume more units, MU declines, but TU keeps
rising
Therefore, we maximize our total utility when our MU falls to
zero
1924
Copyright 2002 by The McGrawHill Companies, Inc. All rights reserved.
Hamburgers Fries Coke
Price QD MU Price QD MU Price OD MU
$ 3.00 1 $3.00 $1.50 1 $1.50 $1.50 1 $1.50
2.00 2 2.00 1.00 2 1.00 .50 2 .50
1.00 3 1.00 .50 3 .50
How many burgers, fries, and cokes would you consume if
burgers were $3, fries were $.50 and cokes were $.50?
Copyright 2002 by The McGrawHill Companies, Inc. All rights reserved.
1925