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Module 02: Markets, Demand, & Supply
Lesson 01/Activity 01
Demand Curves, Movements Along Demand Curves and Shifts in
Demand Curves
Part A
The figure below shows the market demand for a hypothetical product: Greebes. Study the data, and
plot the demand for Greebes on the axes in Figure 9.2 below (insert a suitable line). Label the demand
curve D (insert a small text box), and answer the questions that follow. Write the correct answer in the
answer blanks, or highlight the correct words in parentheses.
Demand for Greebes
Price
($ per Greebe)
$.10
.15
Quantity
Demanded
(millions of
Greebes)
350
300
.20
.25
250
200
.30
.35
150
100
.40
50
The data for demand curve D indicate
that at a price of $.30 per Greebe, buyers
would be willing to buy _____ million
Greebes. CetPar, if the price of Greebes
increased to $.40 per Greebe, buyers
would be willing to buy _____ million
Greebes. Such a change would be a
decrease in (demand or quantity
demanded… which one?). CetPar, if the
price of Greebes decreased to $.20,
buyers would be willing to buy _____
million Greebes. Such a change would be
an increase in (demand or quantity
demanded… which one?).
AP/IB Economics
Lausanne
Year 1, Sem. 1
Module 02: Markets, Demand, & Supply
Lesson 01/Activity 01
Now, let’s suppose there is a dramatic
change in federal income-tax (hyperlink takes you
to a searchable glossary of economic terminology)
rates that affects the disposable income of Greebe
buyers. This change in the CetPar (all else being
equal) assumption underlying the original demand
for Greebes will result in a new set of data, shown
in Figure 9.3 (right). Study these new data, and add
the new demand curve for Greebes to the graph on
the previous page (Figure 9.2). Label the new curve
D1 and answer the questions that follow.
Comparing the new demand curve (D1) with the original demand curve (D), we can say that the change
in the demand for Greebes results in a shift of the demand curve to the (left or right… which one?).
Such a shift indicates that at each of the possible prices shown, buyers are now willing to buy a (smaller
or larger) quantity; and at each of the possible quantities shown, buyers are willing to offer a (higher or
lower) maximum price. The cause (or determinant) of this demand curve shift was a(n) (increase or
decrease) in tax rates that (increased or decreased) the disposable income of Greebe buyers.
Now, let’s suppose that there is a dramatic
change in people’s tastes and preferences for
grebes. This change in the CetPar assumption
underlying the original demand curve for Greebes
will result in a new set of data shown in Figure 9.4
(right). Study these new data, and add the new
demand curve for Greebes to the graph on the
previous page (Figure 9.2). Label the new curve D2
and answer the questions that follow.
Comparing the new demand curve (D2) with the
original demand curve (D), we can say that the change in the demand for Greebes results in a shift of the
demand curve to the (left or right… which one?).
Such a shift indicates that at each of the possible prices shown, buyers are now willing to buy a (smaller
or larger) quantity; and at each of the possible quantities shown, buyers are willing to offer a (higher or
lower) maximum price. The cause (or determinant) of this demand curve shift was a(n) (increase or
decrease) in tax rates that (increased or decreased) the disposable income of Greebe buyers.
AP/IB Economics
Lausanne
Year 1, Sem. 1
Module 02: Markets, Demand, & Supply
Lesson 01/Activity 01
Part B
Now, to test your understanding, underline or highlight the answer you think is the one best alternative
in each of the following multiple-choice questions.
1.
CetPar, which of the following would not cause a change in the demand (shift in the demand
curve) for bicycles?
a.
a decrease in consumer incomes
b.
a decrease in the price of bicycles
c.
an increase in the price of mopeds/scooters
d.
an increase in people’s tastes and preferences for bicycles
2.
“Rising oil prices cause a sharp decrease in the demand for oil.” Speaking precisely, and using
terms as they are defined by economists, choose the statement that best describes this
quotation.
a.
The quotation is correct: an increase in price always causes a decrease in demand.
b.
The quotation is incorrect: an increase in price always causes an increase in demand, not
a decrease in demand.
c.
The quotation in incorrect: an increase in price causes a decrease in the quantity
demanded, not a decrease in demand.
d.
The quotation in incorrect: an increase in price causes an increase in the quantity
demanded, not a decrease in demand.
3.
“As the price of domestic automobiles has inched upward, customers have found foreign autos
to be a better bargain. Consequently, domestic auto sales have been decreasing and foreign
auto sales have been increasing.” Using only the information in this quotation and assuming
everything else constant (CetPar), which of the following best describes this statement?
a.
A shift in the demand curves for both domestic and foreign automobiles.
b.
A movement along the demand curves for both foreign and domestic autos.
c.
A movement along the demand curve for domestic autos, and a shift in the demand
curve for foreign autos.
d.
A shift in the demand curve for domestic autos, and a movement along the demand
curve for foreign autos.
4.
You hear a fellow student say, “Economic markets are like perpetual seesaws. If demand rises,
the price rises; if price rises, then demand will fall. If demand falls, price will fall; if price falls,
demand will rise and so on forever.” Dispel your friend’s obvious confusion in no more than one
short paragraph. Use the space below to type in your response.
AP/IB Economics
Lausanne
Year 1, Sem. 1
Module 02: Markets, Demand, & Supply
Lesson 01/Activity 01
Part C
Once we have the demand curve, we can define the concept of consumer surplus. Consumer surplus is
the value received from the purchase of a good in excess of the price paid for it, or stated differently,
the difference between the amount a person is willing and able to pay and the actual price paid for each
unit.
An approximation of consumer surplus can be shown graphically as the area below the demand curve
above the price paid. Redraw your demand curve from page 1 of this handout on Figure 9.5 below.
If we establish the price of all quantities sold at $.30, then we can show consumer surplus as a shaded-in
area above $.30 up to the demand curve. Try to insert a triangle from the “Insert” dropdown menu
above to show this area. This shaded area represents the area of consumer surplus.
Continue to use the demand curve from the graph on page 1, and assume that the price is established at
$.30. There are buyers who will benefit because they are willing and able to pay higher prices that the
established price of $.30. For example, 50 million Greebes are demanded at $.40, but since the market
price is $.30, there is a gain to the buyers represented by this 50 million. The gain is a total of $5 million
($.10 x 50 million = $5 million). The buyers of the next 50 million Greebes (always consider the extra or
marginal buyers since the buyers at the higher prices will also be willing to buy at a lower price) are
willing to pay $.35, providing a gain of $.05 of the consumer surplus, for a total of $2.5 million.
5.
Approximately what will be the total
consumer surplus for the buyers of the 150 million
Greebes at a price of $.30? ____________________
6.
If the price consumers pay increases, the
shaded area (increases or decreases). If the price
consumers pay decreases, the shaded area
(increases or decreases).
7.
If the equilibrium price drops to $.20, what
will happen to consumer surplus? (increase or
decrease).
8.
At $.20, calculate the consumer surplus for buyers willing to pay:
a.
$.40 _______________________________________
b.
$.35 _______________________________________
c.
$.30 _______________________________________
d.
$.25 _______________________________________
e.
What is the total surplus?
_______________________________________
9.
Will there be any consumer surplus at a price of $.20 for the buyers willing and able to spend
$.20, $.15 or $.10? Why or why not?
AP/IB Economics
Lausanne
Year 1, Sem. 1