Question 604634
A plane flies 900 miles with a tail wind in 3 hours. It takes the same plane 5 hours to fly the 900 miles flying against the wind. What is the plane's speed in still air?
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let x=speed of plane in still air
let c=speed of wind
(x+c)=speed of plane downwind
(x-c)=speed of plane against wind
distance=travel time*speed
..
5(x-c)=900
3(x+c)=900
..
5x-5c=900
3x+3c=900
..
15x-15c=2700 (multi. by 3)
15x+15c=4500 (multi. by 5)
add
30x=7200
x=240
5c=5x-900=300
c=60
ans:
speed of plane in still air=240 mph
speed of wind=60 mph