Algebra Demystified 2nd Ed

342 algebra De mystif ieD

5. 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