45.The graph shows how college stu-
dents managed their money during
the years 1997 through 2004.
(a)During what period did ATM
use dominate both credit card
anddebit card use?
(b)In what year did debit card
use overtake credit card use?
(c)In what year did debit card
use overtake ATM use?
(d)Write an ordered pair for the
debit card use data in the year
1998.
An application of mathematics in economics deals with
supply and demand.Typically, as the price of an item
increases, the demand for the item decreases while the
supply increases. If supply and demand can be de-
scribed by straight-line equations, the point at which
the lines intersect determines theequilibrium supply
andequilibrium demand.
The price per unit, p,and the demand, x,for a particu-
lar aluminum siding are related by the linear equation
,while the supply is given by the linear
equation ,as shown in the figure.
Use the graph to answer the questions in Exercises 46 – 48.
46.At what value of xdoes supply equal demand?
47.At what value of pdoes supply equal demand?
48.When x 740 , does demand exceed supply or does supply exceed demand?
p=^34 x
p= 60 -^34 x
256 CHAPTER 4 Systems of Linear Equations and Inequalities
Percent
‘97 ‘98 ‘99 ‘00 ‘01 ‘02 ‘03 ‘04
20
40
60
80
100
ATM
Credit
Debit
Year
Source: Georgetown University Credit Research Center.
How College Students Manage Their Money
p
SUPPLY AND DEMAND
Price
p = 60 – x (demand)
p = x (supply)
x
3
4
3
4
10
20
30
40
50
70
80
60
080 10 20 30 40 50 60 70
Quantity
EXERCISES 49 – 52
Match the graphing calculator screens in choices A– D with the appropriate system in
Exercises 49 – 52. See the Connections box.
A. B.
C. D.
TECHNOLOGY INSIGHTS
10
–10 10
–10
10
–10 10
–10
10
–10 10
–10
10
–10 10
–10
3 x+ 2 y= 7
x- y= 0
2 x+ 3 y= 5
x-y=- 8
x+y= 6
x-y= 2
x+y= 4
http://www.ebook777.com
http://www.ebook777.com
