SOLUTION: a girl flew her plane for 6 hr at a constant speed. She traveled 810 mi with the wind, then turned around and traveled 720 mi against the wind. The wind speed was a constant 15mph.

Question 587071: a girl flew her plane for 6 hr at a constant speed. She traveled 810 mi with the wind, then turned around and traveled 720 mi against the wind. The wind speed was a constant 15mph. Find the speed of the plane
Answer by lwsshak3(11628) (Show Source): You can put this solution on YOUR website!
a girl flew her plane for 6 hr at a constant speed. She traveled 810 mi with the wind, then turned around and traveled 720 mi against the wind. The wind speed was a constant 15mph. Find the speed of the plane.
**
let x=speed of plane
speed downwind=x+15
speed against the wind=x-15
travel time= distance/speed
..
810/(x+15)+720/(x-15)=6
LCD:(x+15)(x-15)
810(x-15)+720(x+15)=6(x+15)(x-15)=6(x^2-225)
810x-12150+720x+10800=6x^2-1350
1530x-1350=6x^2-1350
6x^2-1530x=0
x^2-255x=0
x(x-255)=0
x=0 (reject)
or
x=255 mph
ans:
speed of plane=255 mph
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