Intermediate Algebra (11th edition)

90.Total sales of fax machines in the United States (in mil-
lions of dollars) are shown in the graph, where the year
2003 corresponds to.
(a)Use the ordered pairs from the graph to write an
equation that models the data. What does the slope
tell us in the context of this problem?
(b)Use the equation from part (a) to approximate the
sales of fax machines in the United States in 2007.

91.Expenditures for home health care in the
United States are shown in the graph.
(a)Use the information given for the years
2003 and 2007, letting represent
2003, represent 2007, and y
represent the amount (in billions of
dollars) to write an equation that models
home health care spending.
(b)Use the equation from part (a) to
approximate the amount spent on
home health care in 2005. How does
your result compare with the actual
value, $48.1 billion?

92.The number of post offices in the
United States is shown in the graph.
(a)Use the information given for the
years 2003 and 2008, letting
represent 2003, represent
2008, and yrepresent the number of
post offices, to write an equation
that models the data.
(b)Use the equation to approximate the
number of post offices in 2006. How
does this result compare with the
actual value, 27,318?

x= 8

x= 3

x= 7

x= 3

x= 0

SECTION 3.3 Linear Equations in Two Variables 173

0231

50

100

150

200

250

x

y

(0, 242)

Year

Sales

(in millions of dollars)

(3, 127)

Source: Consumer Electronics

Association.

Fax Machine Sales

Spending on Home Health Care

Source: U.S. Centers for Medicare &

Medicaid Services.

Year

Billions of Dollars

60

50

40

30

20

10

0

2003 2004 2005 2006 2007

38.0

59.0

U.S. Post Offices

2003 2004 2005 2006 2007 2008

Year

10,000

20,000

30,000

Source: U.S. Postal Service.

Number of Post Offices 0

27,556 27,232

EXERCISES 93 – 100

FOR INDIVIDUAL OR GROUP WORK

In Section 2.2,we worked with formulas. Work Exercises

93–100 in order,to see how the formula that relates Celsius

and Fahrenheit temperatures is derived.

93.There is a linear relationship between Celsius and

Fahrenheit temperatures. When , °,

and when , °.

94.Think of ordered pairs of temperatures , where C

and Frepresent corresponding Celsius and Fahrenheit

temperatures. The equation that relates the two scales has a straight-line graph that

contains the two points determined in Exercise 93.What are these two points?

95.Find the slope of the line described in Exercise 94.

1 C, F 2

C=100° F=

C=0°F=

RELATING CONCEPTS

(continued)