342 algebra De mystif ieD
- Let x represent the number of minutes the call lasts. Let c = 2.10 + 0.50x
represent the total cost of the call.
450210 050600
210210
≤+ ≤
--
x
- ≤≤
≤≤
210
240050 390
240
050
050
050
x
x 3390
050
48 78
..≤≤x
4.8 minutes is 4 minutes 48 seconds and 7.8 minutes is 7 minutes
48 seconds because 0.80 minutes is 0.80(60) seconds = 48 seconds.
A call would need to last between 4 minutes 48 seconds and 7 minutes
48 seconds in order to cost between $4.50 and $6.00.
Summary
In this chapter, we learned how to:
• Represent an inequality as a region on the number line and with interval
notation. Figure 9-19 shows the relationship between an unbounded
interval, its region on the number line, and its representation as an
interval.
Inequality Number Line Region Interval Notation
x < a (–∞, a)
(–∞, a]
(a, ∞)
[a, ∞)
x ≤ a
x > a
x ≥ a
a
a
a
a
FIgure 9-19