Question:In a stream running at 2 kmph, a motorboat goes 6 km upstream and back again to the starting point in 33 minutes. Find the speed of the motorboat in still water. 

Answer Let the speed of the motorboat in still water be x kmph.

Then, speed downstream = (x + 2) kmph.

Speed upstream = (x - 2) kmph

`:. 6/(x + 2) + 6/(x - 2)`

`= 33/60 or 11x^2 - 240x - 44 = 0`

`:. 11x^2 - 242x + 2x - 44 = 0`

`or 11x (x - 22) + 2 (x - 22) = 0`

`or (x - 22) (11x + 2) = 0 or x = 22`

:. Speed of motorboat in still water = 22 kmph. 

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