In stream running at 4 kmph a motorboat goes 6 km upstream and back again to the starting point in 2...........

Quant (SSC) Boats and Streams

In stream running at 4 kmph, a motorboat goes 6 km upstream and back again to the starting point in 2 hours. Find the speed of the motorboat in still water.

12 km/h

8 km/h

11 km/h

4 km/h

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Explanation:

Let the speed of the motorboat in still water be x kmph.
Then, Speed downstream = (x + 4) kmph;
Speed upstream = (x – 4) kmph.
∴ 6 /(x + 4) + 6 /(x - 4) = 2
Now by taking option B
⇒ Putting x = 8, we get
6/12 + 6/4 = 2
1/2 + 3/2 = 2
2 = 2