Precalculus (6th Edition) Blitzer

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

Chapter 7 - Section 7.1 - Systems of Linear Equations in Two Variables - Exercise Set - Page 819: 61

Answer

The average velocity of the plane in still air is $130$ mph and that of the wind is $30$ mph.

Work Step by Step

Step 1. Assume the average velocity of the plane in still air is $x$ mph and that of the wind $y$ mph. Step 2. When flying with the wind, the total average velocity is $x+y$; thus $5(x+y)=800$ or $x+y=160$ Step 3. When flying against the wind, the resulting average velocity is $x-y$; thus $8(x-y)=800$ or $x-y=100$ Step 4. Adding the two equations, we get $2x=260$; thus $x=130$ mph and $y=30$ mph.
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