Intermediate Algebra (11th edition)

86.The upper deck at U.S. Cellular Field in Chicago
has produced, among other complaints, displeas-
ure with its steepness. It is 160 ft from home plate
to the front of the upper deck and 250 ft from
home plate to the back. The top of the upper deck
is 63 ft above the bottom. What is its slope? (Con-
sider the slope as a positive number here.)

SECTION 3.2 The Slope of a Line 159

150 ft

250 ft

63 ft 160 ft

Cellular Phone Subscribers

2005 2008

280

240

220

200

x

y

Year

Subscribers(in millions)

(2005, 207.3)

(2008, 270.9)

0

260

Source: CTIA: The Wireless

Association.

(2005, 79.5)

Spending on Personal

Care Products

2005 2008

70

80

90

100

x

y

Year

Spending

(in billions of dollars)

(2008, 91.3)

0

Source: U.S. Department of

Commerce.

Drive-In Theaters

2000 2002 2004 2006

Year

(2000, 443)

(2007, 405)

Number

400

420

440

460

0

Source: http://www.drive-ins.com

Solve each problem. See Examples 9 and 10.

89.The graph provides a good approximation of
the number of drive-in theaters in the United
States from 2000 through 2007.
(a)Use the given ordered pairs to find the
average rate of change in the number of
drive-in theaters per year during this
period. Round your answer to the nearest
whole number.
(b)Explain how a negative slope is interpreted
in this situation.

Concept Check Solve each problem.

85.When designing the arena now known as TD
Banknorth Garden in Boston, architects designed
the ramps leading up to the entrances so that cir-
cus elephants would be able to walk up the ramps.
The maximum grade (or slope) that an elephant
will walk on is 13%. Suppose that such a ramp
was constructed with a horizontal run of 150 ft.
What would be the maximum vertical rise the
architects could use?

(a)Use the given ordered pairs to find

the slope of the line.

(b)Interpret the slope in the context of

this problem.

(a)Use the given ordered pairs to find the

slope of the line to the nearest tenth.

(b)Interpret the slope in the context of

this problem.

87.The graph shows the number of cellular
phone subscribers (in millions) in the
United States from 2005 to 2008.

88.The graph shows spending on personal

care products (in billions of dollars) in

the United States from 2005 to 2008.