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River is running at 2 kmph. It took a man twice as long to row up as to row down the river. The. rate (in km ph) of the man in still water is :

 A) 8 B) 10 C) 4 D) 6

 D) 6

Let rate upstream be kmph

Then, rate downstream = 2x kmph

$$\Large \therefore$$ Rate of current

$$\Large \frac{1}{2} (2x - x) = \frac{x}{2} \ kmph$$

$$\Large \therefore \frac{x}{2} = 2 => x = 4$$

$$\Large \therefore$$ Rate upstream = 4 kmph

Rate downstream = 8 kmph

$$\Large \therefore$$ Rate in still water

= $$\Large \frac{1}{2} (8 + 4) = 6 \ kmph$$

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