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Change in Demand vs. Change in Quantity Demand
Be
Careful!
• You can not have both an:
– Increase in demand and an increase in quantity demanded
–
or
– Increase in supply and an increase in quantity supplied
The same is true for a decrease….
Change in Demand
Increase in Demand
Price
Decrease in Demand
D1
Qty
T-Shirts
Curves only shift when
a determinant changes
(TIPSEN or TINE TP)
Change in Quantity Demanded
Price
Ice Cream makers raise prices to 200
$2.00
leads to
B
movement along existing demand curve
Called a Change in
Quantity Demanded
A
1.00
D
0
4
Ice Cream
8
Quantity
Test: How would you describe the change:
Price
P1
------------------- E2
-------------- E1
------------------------------
P2
S1
Q1 Q2
Soda
D1
D2
Qty
Summary
• ONLY when a determinant of demand or determinant
of supply changes can you have a:
– Increase or decrease in demand [TIPSEN]
– Increase or decrease in supply [TINE & TP]
• When price only changes
– There is a change in quantity demanded
[only price]