A boat goes 25 km upstream and 35 km downstream in 10 hours. In 15 hours, it can go 40 km upstream and 49 km downstream. Determine the speed of the stream and that of the boat in still water.

Explanation

Let spped of water is `x` km/h and speed of stream is `y` km/h.

Then, speed at upstream `= x-y` km/h

Speed at downstream ` = x+y` km/h

Case -1 : `25/(x-y)+35/(x+y) = 10`

`=>5/(x-y)+7/(x+y) = 2->(1)`

Case-2 : `40/(x-y)+49/(x+y) = 15->(2)`

Let `1/(x-y) = a, 1/(x+y) = b`

So, the equation (1) and (2) becomes,

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