SOLUTION: A plane traveled 864 miles to Shanghai and back. The trip there was with the wind. It took 9 hours. The trip back was into the wind. The trip back took 18 hours. What is the speed

Question 498948: A plane traveled 864 miles to Shanghai and back. The trip there was with the wind. It took 9 hours. The trip back was into the wind. The trip back took 18 hours. What is the speed of the plane in still air? What is the speed of the wind?
Answer by mananth(16946) (Show Source): You can put this solution on YOUR website!
Plane speed =x mph
Wind speed =y mph
against wind x-y 18.00 hours
with windx+y 9.00 hours

Distance = same= 864 miles
t=d/r
864 / ( x - y )= 18.00
18 ( x - y ) = 864.00
18 x -18 y = 864 ....................1
864 / ( x + y )= 9.00
9.00 ( x + y ) = 864
9.00 x + 9.00 y = 864 ...............2
Multiply (1) by 1.00
Multiply (2) by 2.00
we get
18 x + -18 y = 864
18 x + 18 y = 1728
36 x = 2592
/ 36
x = 72 mph

plug value of x in (1)
18 x -18 y = 864
1296 -18 y = 864
-18 y = 864 -1296
-18 y = -432
y = 24 mph

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