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AP ECONOMICS – CHAPTER 5
Consumer Behavior and Utility Maximization
4 Key Concepts
1. Understanding Utility: Total and Marginal2. Utility Maximization: Equalizing Marginal
Utility per Dollar (MU/PA = MU/PB)
3. Individual and Market Demand Curves4. Income and Substitution Effects (review
from unit two)
Introduction
The CONSUMER is essential to the market. Understanding how the consumer makes his/her purchasing decisions is key.
1. Understanding Utility
Utility = Satisfaction/Happiness/Pleasure one gets from consuming a good.
Utility and usefulness are NOT synonymous in economics.
Utility is difficult to quantify, as it differs between people and situations ie. A blanket to a person living in Arizona vs. a
person living in Minnesota.
Measured in “utils” (a personal measure)
1. Understanding Utility
Total Utility (TU) Total amount of satisfaction or pleasure a person
derives from consuming a given quantity of that product
Marginal Utility (MU) The extra satisfaction a consumer derives from one
additional unit of that product. In other words, the change in Total Utility that
results from the consumption of one more unit
Law of Diminishing Marginal Utility
Explains that the more of a good a person gets, the less utility he gets from each additional unit.
Consumer wants in general are insatiable, but wants for particular items can be satisfied for a time. Example: Durable goods such as an automobile
First is the Best
It is important to note that your marginal utility begins to fall after the very first unit you consume.
In other words, your very first taco holds great utility. While you may enjoy your second taco, it doesn’t bring as much utility as the first
At some point, your MU becomes negative. (takes away from your total satisfaction).
Law of Diminishing Marginal Utility
0
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To
tal U
tilit
y (U
tils
)M
arg
inal
Uti
lity
(Uti
ls)
(1)Tacos
ConsumedPer Meal
(2)Total
Utility,Utils
(3)MarginalUtility,Utils
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TU
MU
Total Utility
Marginal Utility
Units Consumed Per Meal
Units Consumed Per Meal
2. Utility Maximization
Explains how consumers allocate their money incomes among the many goods and services available for purchase
You will be faced with problems that provide you with a consumer’s MU or TU derived from purchasing 2 goods. You will be expected to show how many of each a rational consumer would purchase.
Theory of Consumer BehaviorNumerical Example:Find the Utility-Maximizing Combination of A and B, if you have an Income of $10
(1)Unit of
Product
(a)MarginalUtility,Utils
(a)MarginalUtility,Utils
(b)Marginal
UtilityPer Dollar(MU/Price)
(b)Marginal
UtilityPer Dollar(MU/Price)
(2)Product A:Price = $1
(3)Product B:Price = $2
First
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Seventh
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Theory of Consumer Behavior
Numerical Example:Utility-Maximizing Combination of Products A and B Obtainable with an Income of $10
(1)Unit of
Product
(a)MarginalUtility,Utils
(a)MarginalUtility,Utils
(b)Marginal
UtilityPer Dollar(MU/Price)
(b)Marginal
UtilityPer Dollar(MU/Price)
(2)Product A:Price = $1
(3)Product B:Price = $2
First
Second
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Fifth
Sixth
Seventh
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Compare Marginal UtilitiesThen Compare Per Dollar - MU/PriceChoose the HighestCheck Budget - Proceed to Next Item
Theory of Consumer BehaviorNumerical Example:Utility-Maximizing Combination of Products A and B Obtainable with an Income of $10
(1)Unit of
Product
(a)MarginalUtility,Utils
(a)MarginalUtility,Utils
(b)Marginal
UtilityPer Dollar(MU/Price)
(b)Marginal
UtilityPer Dollar(MU/Price)
(2)Product A:Price = $1
(3)Product B:Price = $2
First
Second
Third
Fourth
Fifth
Sixth
Seventh
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20
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16
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10
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Again, Compare Per Dollar - MU/PriceChoose the HighestBuy One of Each – Budget Has $5 LeftProceed to Next Item
Theory of Consumer BehaviorNumerical Example:Utility-Maximizing Combination of Products A and B Obtainable with an Income of $10
(1)Unit of
Product
(a)MarginalUtility,Utils
(a)MarginalUtility,Utils
(b)Marginal
UtilityPer Dollar(MU/Price)
(b)Marginal
UtilityPer Dollar(MU/Price)
(2)Product A:Price = $1
(3)Product B:Price = $2
First
Second
Third
Fourth
Fifth
Sixth
Seventh
10
8
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5
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20
18
16
12
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10
9
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Again, Compare Per Dollar - MU/PriceBuy One More B – Budget Has $3 LeftProceed to Next Item
Theory of Consumer BehaviorNumerical Example:Utility-Maximizing Combination of Products A and B Obtainable with an Income of $10
(1)Unit of
Product
(a)MarginalUtility,Utils
(a)MarginalUtility,Utils
(b)Marginal
UtilityPer Dollar(MU/Price)
(b)Marginal
UtilityPer Dollar(MU/Price)
(2)Product A:Price = $1
(3)Product B:Price = $2
First
Second
Third
Fourth
Fifth
Sixth
Seventh
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20
18
16
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10
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2
Again, Compare Per Dollar - MU/PriceBuy One of Each – Budget Exhausted
Theory of Consumer BehaviorNumerical Example:Utility-Maximizing Combination of Products A and B Obtainable with an Income of $10
(1)Unit of
Product
(a)MarginalUtility,Utils
(a)MarginalUtility,Utils
(b)Marginal
UtilityPer Dollar(MU/Price)
(b)Marginal
UtilityPer Dollar(MU/Price)
(2)Product A:Price = $1
(3)Product B:Price = $2
First
Second
Third
Fourth
Fifth
Sixth
Seventh
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6
5
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20
18
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Final Result – At These Prices, Purchase 2 of Item A and 4 of B
Theory of Consumer BehaviorAlgebraic Restatement:
MU of Product A
Price of A
MU of Product B
Price of B=
8 Utils
$1
16 Utils
$2=
Optimum Achieved - Money Income is Allocated so that the Last Dollar
Spent on Each Good Yields the Same Extra or Marginal Utility
Two-Good Practice ProblemGiven MU, and an income/budget constraint of $20… find the Utility-Maximizing Combination of A and B
(2)Product A:Price = $2
(3)Product B:Price = $5
Unit MU Unit MU
1 20 1 30
2 10 2 20
3 6 3 15
4 3 4 5
5 1 5 -5
(2)Product A:Price = $2
(3)Product B:Price = $1
Unit TU Unit TU
1 22 1 10
2 32 2 16
3 40 3 20
4 46 4 22
5 48 5 20
Given TU, and an income/budget constraint of $9… find the Utility-Maximizing Combination of A and B
Two-Good Practice Problem
The Problem with Utils
Answer the following problem:If Henry derives 5 utils from the 1st candy
bar, 3 utils from the 2nd candy bar, 0 utils from the 3rd candy bar, and -5 utils from the 4th candy bar… How many candy bars should Henry consume if
each candy bar … Is absolutely free (MC = 0) Costs $2 Costs $4
From ‘Utils’ to ‘Benefit’
Because Utils cannot be compared between people, and cannot be compared to dollars… economists must measure satisfaction in Benefit. Benefit is the same concept as utility, but it is
measured in dollars (according to the consumer’s WILLINGNESS TO PAY.
Total Benefit ($), Marginal Benefit ($)
Golden Rule of Consumption
Start with an individual consumer maybe you, maybe me, but could be anyone
Derive demand curve for that individual focus on marginal utility or marginal benefit
Add up demand curves for many such individuals to get market demand curve
3. Individual and Market Demand Curves
Assumption about consumer behavior
General economic principle People make purposeful
choices with limited
resources
When applied to the behavior of consumers People maximize utility subject to a budget
constraint
3. Individual and Market Demand Curves
Consider all consumers in the marketAdd up quantity demanded by all individuals
at each price to get market demandAdd horizontally to create market demand
curve
05_06
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QUANTITY DEMANDEDBY PETE (POUNDS)
QUANTITY DEMANDED
BY ANN (POUNDS)
QUANTITY DEMANDED
IN MARKET (POUNDS)
PRICE(DOLLARS)
PRICE(DOLLARS)
PRICE(DOLLARS)
Marketdemandcurve
Ann'sdemandcurve
Pete'sdemandcurve
4. Substitution and Income Effects
This topic on the AP Course Outline was already covered in unit 2.
To review, just remember that both of these effects help to explain why the demand curve slopes downward.
Review Questions – Utility
Which of the following factors contributes to a downward-sloping demand curve? I. The income effect II. The substitution effect III. Diminishing marginal utility
A. I onlyB. III onlyC. I and II onlyD. II and III onlyE. I, II, and III
Review Questions – Utility
What is the marginal utility of the third cup of peanuts Brian consumes?
A. 3 units of utilityB. 9 units of utilityC. 12 units of utilityD. 2 units of utilityE. 14 units of utility
Review Questions – Utility
If the price of peanuts is $1 per cup and the price of jelly beans is $2 per cup, and Brian wants to maximize his utility, what should he purchase first?
A. 1 cup of peanuts because peanuts produce a lower total utility
B. 1 cup of peanuts because the price of peanuts is lower
C. 1 cup of peanuts, because the marginal utility per dollar for peanuts is lower than the marginal utility per dollar of jelly beans
D. 1 cup of jelly beans, because the marginal utility per dollar for jelly beans is higher than the marginal utility per dollar of peanuts
E. 1 cup of jelly beans, because jelly beans produce a higher total utility
Review Questions – Utility
If TU = total utility, MU = marginal utility, and P = price, in order to maximize utility, a consumer should purchase the mix of hamburgers and hot dogs where
A. the MU of hamburgers equals the MU of hot dogs
B. the MU equals the TU of hamburgers, and the MU equals the TU of hot dogs
C. the TU of hamburgers equals the TU of hot dogsD. the MU / P of hamburgers equals the MU / P of
hot dogsE. the TU / P of hamburgers equals the TU / P of
hot dogs
Review Questions – Utility
If Matt’s total utility from consuming slices of cheese increased at a constant rate, no matter how many bratwurst Matt consumed, what would Matt’s demand curve for slices of cheese look like?
A. VerticalB. HorizontalC. Downward slopingD. Upward slopingE. First upward, but eventually downward
sloping
Review Questions – Utility
Every day Molly spends her lunch money consuming apples, at $1 each, and oranges, at $2 each. At her current level of consumption, molly’s marginal utility of apples is 12 and her marginal utility of oranges is 18. If she has already spent all of her lunch money, how should Molly change her consumption decision to maximize utility?
A. She should make no changes; she is consuming the utility maximizing combination of apples and oranges.
B. She should increase her apple consumption and decrease her orange consumption until the marginal utility per dollar is equal for both.
C. She should decrease her apple consumption and increase her orange consumption until the marginal utility per dollar is equal for both.
D. She should increase her apple consumption and decrease her orange consumption until the marginal utility is equal for both.
E. She should decrease her apple consumption and increase her orange consumption until the marginal utility is equal for both.
Review Questions – Utility
If generic peanut butter is an inferior good, a decline in consumer income causes
A. the price of generic peanut butter to go down.B. the demand for name-brand peanut butter to
go up.C. the supply of generic peanut butter to go up.D. the demand for generic peanut butter to go
up.E. the price of bread to go down.
Key Terms
law of diminishing marginal utility
utilitytotal utilitymarginal utilityrational behaviorbudget constraintutility-maximizing ruleincome effectsubstitution effect
Pri
ce
of
Pro
du
ct
B
0
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4 6
Quantity Demanded of B
Deriving the Demand CurveSame Numeric Example:
$2
1
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Price Per Unit of B
QuantityDemanded
DBIncome Effects
Substitution Effects