Intermediate Algebra (11th edition)

80.Sharon Kobrin compared the monthly pay-
ments she would incur for two types of
mortgages: fixed rate and variable rate. Her
observations led to the following graphs.
(a)For which years would the monthly
payment be more for the fixed-rate
mortgage than for the variable-rate
mortgage?
(b)In what year would the payments be
the same, and what would those
payments be?

81.The graph shows sales (in millions of
dollars) in the United States of three types
of television displays from 2003 through
2008.
(a)During what years did sales of plasma
flat panel displays exceed those of
front projection displays?
(b)Between what two consecutive years
did LCD flat panel first become the
most popular type of display?
(c)When were sales of LCD flat panel
and plasma flat panel displays approx-
imately equal? What were sales at that
time?
(d)Write your answer for part (c) as an ordered pair, rounding down to the nearest year.
(e)Describe the trends in sales of the three types of displays during the years shown.

82.The graph shows the numbers of non-Hispanic whites and African-Americans (in thou-
sands) living with AIDS in the United States during the period 1995 through 2007.

SECTION 4.1 Systems of Linear Equations in Two Variables 223

Year

0

600

650

700

Mortgage Shopping

Monthly Payment

(in dollars)

4128 16

Fixed

Variable

Year

Sales

(in millions of dollars)

‘03 ‘04 ‘05 ‘06 ‘07 ‘08

0

3000

6000

9000

12,000

15,000

18,000

Looking at the Tube

Source: Consumer Electronics Association.

Plasma

Flat Panel

LCD Flat Panel

Front Projection

People Living with AIDS

180

200

Number (in thousands)

160

140

120

100

80

60

0

‘95 ‘96 ‘97 ‘98 ‘99 ‘00 ‘01 ‘02 ‘03 ‘04 ‘05 ‘06 ‘07

Source: U.S. Centers for Disease Control and Prevention.

Year

African-American

White

(a)In what year were the numbers approximately the same?

(b)How many people of each race were living with AIDS in that year?

(c)Express the point of intersection of the graphs for whites and African-Americans

living with AIDS as an ordered pair of the form (year, number).

(d)During what two consecutive years did the number of whites living with AIDS first

stabilize and remain fairly constant?

(e)Describe the trend in the number of African-Americans living with AIDS from 1995

through 2007. If a straight line were used to approximate its graph, would the line

have a positive, negative, or 0 slope?