77.For a certain provider, an international phone call costs $2.00 for the first 3 min, plus
$0.30 per minute for each minute or fractional part of a minute after the first 3 min. If
xrepresents the number of minutes of the length of the call after the first 3 min, then
represents the cost of the call. If Alan Lebovitz has $5.60 to spend on a call,
what is the maximum total time he can use the phone?
78.At the Speedy Gas’n Go, a car wash costs $4.50 and gasoline is selling for $3.20 per gal-
lon. Carla Arriola has $38.10 to spend, and her car is so dirty that she must have it
washed. What is the maximum number of gallons of gasoline that she can purchase?
A company that produces DVDs has found that revenue from the sales of the DVDs is $5per
DVD, less sales costs of $100.Production costs are $125,plus $4per DVD. Profit (P) is given
by revenue (R) less cost (C), so the company must find the production level x that makes
that is,
79.Write an expression for revenue R, letting xrepresent the production level (number of
DVDs to be produced).
80.Write an expression for production costs Cin terms of x.
81.Write an expression for profit P, and then solve the inequality
82.Describe the solution in terms of the problem.
Concept Check Write a three-part inequality involving the variable x that describes each
set of numbers graphed.
85. 86.
Write each inequality in interval notation, and graph the interval. See Example 7.
Solve each inequality. Write the solution set in interval notation, and graph it. See Example 8.
101. 102.
103. 104.- 12 ...
3
7
5
4
r- 1 ...- 1
266 +
3
4
1 ... 3 + x 612
2
3
p... 7
- 6 ... 3 +
1
3
1
2
z+ 1 ... 4
1067 p+ 3624 - 8 ... 3 r- 1 ...- 1
561 - 6 m 612 - 1 ... 1 - 5 q... 16
- 5 ... 2 x- 3 ... 9 - 7 ... 3 x- 4 ... 8
- 3 ...x 60 47 x7- 3 6 ÚxÚ- 4
8 ...x... 10 3 ...x... 5 06 y... 10
P 7 0.
P 7 0, R-C 7 0. P=R-C
2 +0.30x
162 CHAPTER 2 Linear Equations and Inequalities in One Variable
–1 0 1 2 –1 0 1 2
–1 0 1 2 –1 0 1 2
Find the value of y when (a) and (b). See Sections 1.3 and 2.3.
- 4 x+ 7 y= 11 109. 2 x- 5 y= 10 110.y+ 3 x= 8
y= 5 x+ 3 y= 4 - 3 x 6 x- 2 =y
x=- 2 x= 4
PREVIEW EXERCISES
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