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 mph, what is the speed of the plane in still air?
A) 256 mph
B) 236 mph
C) 231 mph
D) 221 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 420/(x + 21) = 350/(x - 21). Solving this equation gives x = 231 mph.

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