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ModULE 1.4
FIGURE 1.4-5 Individual demand Curves and the Market demand Curve

(a) Darla’s Individual (b) Dino’s Individual (c) Market Demand Curve
Demand Curve Demand Curve
Price of Price of Price of
blue blue blue
jeans jeans jeans
(per pair) (per pair) (per pair)

$30 $30 $30

D Market

D Darla D Dino
0 3 0 2 0 5
Quantity of blue jeans Quantity of blue jeans Quantity of blue jeans
(pairs) (pairs) (pairs)
Darla and Dino are the only two consumers of blue jeans in the consumers at any given price, is shown in panel (c). The market
market. Panel (a) shows Darla’s individual demand curve: the demand curve is the horizontal sum of the individual demand
number of pairs of jeans she will buy per year at any given price. curves of all consumers. In this case, at any given price, the
Panel (b) shows Dino’s individual demand curve. Given that quantity demanded by the market is the sum of the quantities
Darla and Dino are the only two consumers, the market demand demanded by Darla and Dino.
curve, which shows the quantity of blue jeans demanded by all

demand curve, D Dino , is shown in panel (b). Panel (c) shows the market demand curve.
At any given price, the quantity demanded by the market is the sum of the quantities
demanded by Darla and Dino. For example, at a price of $30 per pair, Darla demands
three pairs of jeans per year and Dino demands two pairs per year. So the quantity
demanded by the market is five pairs per year.
Clearly, the quantity demanded by the market at any given price is larger with Dino
present than it would be if Darla were the only consumer. The quantity demanded at
any given price would be even larger if we added a third consumer, then a fourth, and
so on. So an increase in the number of consumers leads to an increase in demand.

Adventures in
®
AP Economics
Module 1.4 Review Watch the video:
Demand

Check Your Understanding

1. Explain whether each of the following events represents c. People buy more long-stem roses the week of
(i) a change in demand (a shift of the demand curve) or Valentine’s Day, even though the prices are higher
(ii) a movement along the demand curve (a change in the than at other times during the year.
quantity demanded). d. A sharp rise in the price of gasoline leads many
a. A store owner finds that customers are willing to pay commuters to join carpools in order to reduce their
more for umbrellas on rainy days. gasoline purchases.
b. When XYZ Mobile, a cellular plan provider, offered
reduced rates on data charges, its volume data usage
by users increased sharply.

Module 1.4 Review 35
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