algebra
posted by Libuse .
An airplane flying with the wind can cover a certain distance in a = 3 hours. The return trip against the wind takes b = 4.5 hours. How fast is the plane and what is the speed of the wind, if the oneway distance is c = 720 miles?

speed of plane in no wind  x mph
speed of wind  y mph
time with the wind = 720/(x+y) = 3
3x + 3y = 720
x + y = 240
time against the wind = 720/(xy) = 4
4x  4y = 720
xy = 180
add the two simplified equations:
2x = 420
x = 210
back in x+y=240
210 + y = 240
y = 30
the plane has a speed of 210 mph, and the wind was 30 mph 
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