The rate of the plane in still air is 870km/h and the rate of the wind 210km/h.
Speed has the dimensions of distance divided by time.
Let Speed of airplane be x km/h and Speed of Wind be y km/h
Speed direction of wind (x+y)
Speed in opposition of wind (x-y)
Now, using speed x time= distance
7( x-y)=4620
(x-y)=4620/7
=660------------------(1)
Similarly,
8(x+y)=8640
(x+y) =8640/8=1080-----------------------(2)
Adding (1) and (2)
2x=1740
x=870 km/h
Subtracting (1) from (2)
2y=420
=>y=210 km/h
So rate of airplane =870km/h
rate of wind=210km/h
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