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# A person can row a boat d km upstream and the same distance downstream in $$\Large 5 \frac{1}{4} \ hours$$. Also he can row the boat 2d km upstream in 7 hours. He will row the same distance downstream in

 A) $$\Large 3 \frac{1}{2} \ hours$$ B) $$\Large 3 \frac{1}{4} \ hours$$ C) $$\Large 4 \frac{1}{4} \ hours$$ D) 4 hours

 A) $$\Large 3 \frac{1}{2} \ hours$$

Let the speed of boat in still water he x kmph and that of current by y kmph.

According to the question,

$$\Large \therefore \frac{d}{x + y} + \frac{d}{x - y} = \frac{21}{4}$$ ... (i)

and, $$\Large \frac{2d}{x - y} = 7 => \frac{d}{x - y} = \frac{7}{2}$$ ...(ii)

By equation (ii) - (i),

$$\Large \frac{d}{x + y} = \frac{21}{4} - \frac{7}{2} = \frac{21 - 14}{4} = \frac{7}{4}$$

=> $$\Large \frac{2d}{x + y} = \frac{7}{2} = 3 \frac{1}{2} hours$$

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