Algebra 2 (1st Edition)

Published by McDougal Littell
ISBN 10: 0618595414
ISBN 13: 978-0-61859-541-9

Chapter 2 Linear Equations and Functions - 2.2 Find Slope and Rate of Change - 2.2 Exercises - Problem Solving - Page 88: 49

Answer

$28.8$ miles per gallon

Work Step by Step

The average full efficiency for all the driving is: $$\text{Average efficiency}=\dfrac{\text{total distance}}{\text{total amount of gasoline}}.$$ The total distance is $d$. The amount of gasoline used on the distance traveled in highway driving is $(d/2)/36=d/72$, and the distance traveled in city driving is $(d/2)/24=d/48$. Calculate the average efficiency: $$\dfrac{d}{\dfrac{d}{72}+\dfrac{d}{48}}=\dfrac{d}{\dfrac{48d+72d}{72\cdot 48}}=\dfrac{d}{\dfrac{120d}{3456}}=\dfrac{3456}{120}=28.8.$$ So the average fuel efficiency is $28.8$ miles per gallon.
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