Solve.
-A plane flies 420 miles with the wind and 350 miles against the wind in the same length of time. If the speed of the wind is $21 \mathrm { mph }$, what is the speed of the plane in still air?
A) $256 \mathrm { mph }$
B) $236 \mathrm { mph }$
C) $231 \mathrm { mph }$
D) $221 \mathrm { mph }$

Question

Quizplus · Accepted Answer

Let the speed of the plane in still air be $ x $ mph. With the wind, the plane's speed is $ x + 21 $ mph, and against the wind, it is $ x - 21 $ mph. The time taken for both journeys is the same, so $\frac{420}{x + 21} = \frac{350}{x - 21}$. Solving this equation gives $ x = 231 $ mph.

Solve -A Plane Flies 420 Miles with the Wind and 350

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-A Plane Flies 420 Miles with the Wind and 350