Question 603093
1)A plane traveled 630 miles to Tokyo and back. The trip there was with the wind.It took 7 hours. The trip back was into the wind. The trip back took 21 hours. What is the speed of a plane in still air? what is the speed of the wind?
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let x=speed of plane in still air
let c=speed of wind
(x+c)=net speed of plane with wind
(x-c)=net speed of plane into wind
distance=travel time*speed
..
7(x+c)=630
21(x-c)=630
..
7x+7c=630
21x-21c=630
..
21x+21c=1890
21x-21c=630
add, eliminating c
42x=2520
x=2520/70=60
7c=630-7x=630-420=210
c=30
..
ans:
speed of plane in still air=60 mph 
speed of wind=30 mph
..
50 mph for plane speed seems a bit slow for this type of problem