College Algebra 7th Edition

Published by Brooks Cole
ISBN 10: 1305115546
ISBN 13: 978-1-30511-554-5

Chapter 5, Systems of Equations and Inequalities - Section 5.1 - Systems of Linear Equations in Two Variations - 5.1 Exercises - Page 447: 65

Answer

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Work Step by Step

Speed of the man $x$ Speed of the wind $y$ Speed when flying in a head wind $x-y$ Speed when flying back $x+y$ -Speed flying in a head wind $\times$ time flying in a head wind $=$ distance flown in a head wind. $(x-y)\times2=180$. -Speed flying back $\times$ time flying back $=$ distance flown back. $(x+y)\times\frac{6}{5}=180$. Therefore, $\begin{cases} 2x-2y=180\\ \frac{6}{5}x+\frac{6}{5}y=180 \end{cases}$ Multiplying the second equation by 5. $\begin{cases} 2x-2y=180\\ 6x+6y=900 \end{cases}$ Multiplying the first equation by 3 and adding it together. $\begin{cases} 6x-6y=540\\ 6x+6y=900\\ -- -- -- -\\ 12x=1440 \end{cases}$ Thus, $x=120$. Substituting back in $\frac{240-180}{2}=y, y=30$
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