Precalculus (6th Edition) Blitzer

Published by Pearson
ISBN 10: 0-13446-914-3
ISBN 13: 978-0-13446-914-0

Chapter 1 - Section 1.2 - Basics of Functions and Their Graphs - Exercise Set - Page 180: 132


We get the value of $C\left( 100 \right)=\$36$.

Work Step by Step

$C\left( t \right)=20+0.4\left( t-60 \right)$ Where $C\left( t \right)$ is the monthly cost in dollars and $t$ is calling minutes. For $t=100$: $\begin{align} & C\left( 100 \right)=20+0.4\left( 100-60 \right) \\ & =20+0.4\left( 40 \right) \\ & =20+16 \\ & =36 \end{align}$ Thus, for 100 calling minutes, the monthly cost is $36.
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