Precalculus (6th Edition) Blitzer

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

Chapter 7 - Test - Page 879: 14

Answer

The average velocity of the plane is $\text{725 }{\text{km}}/{\text{h}}\;$ and the average velocity of the wind is $\text{75 }{\text{km}}/{\text{h}}\;$.

Work Step by Step

Consider the average velocity of the plane to be $ x $ and the average velocity of the wind to be $ y $. The average velocity of the plane in the direction of the wind is $ x+y $ and the average velocity against the wind is $ x-y $. A plane takes $2$ hours to travel $1600\text{ km}$ in the direction of wind and it takes $3$ hours to travel $1950\text{ km}$ against the direction of wind. The equations from the table give: $\begin{align} & 2\left( x+y \right)=1600 \\ & x+y=800 \end{align}$ …… (1) And $\begin{align} & 3\left( x-y \right)=1960 \\ & x-y=650 \end{align}$ …… (2) Add equation (1) and equation (2). $\begin{align} & \underline{\begin{align} & x+y=800 \\ & x-y=650 \end{align}} \\ & 2x\text{ }=1450 \\ & \text{ }x\text{ }=725 \\ \end{align}$ Substitute $ x=725$ in equation (1). $\begin{align} & x+y=800 \\ & 725+y=800 \\ & y=800-725 \\ & y=75 \end{align}$ Therefore, the average velocity of the plane is $\text{725 }{\text{km}}/{\text{h}}\;$ and the average velocity of the wind is $\text{75 }{\text{km}}/{\text{h}}\;$.
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