Question 783523
A plane flies 460 miles with the wind and 310 miles against the wind in the same length of time. If the speed of the wind is 30 mph, what is the speed of the plane in calm air?
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let x=speed of plane in calm air
x+30=speed of plane downwind
x-30=speed of plane against the wind
travel time=distance/speed (same both directions)
{{{460/(x+30)=310/(x-30)}}}
460(x-30)=310(x+30)
460x-13800=310x+9300
150x=23100
x=154
speed of plane in calm air=154 mph