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A boat can travel 4.2 km upstream in 14 minutes. If the respective ratio of speed of the boat in still water and speed of the stream is 7 : 1. How much time will the boat take to cover 17.6 km downstream ? (in minutes)

 A) 52 B) 44 C) 48 D) 36

 B) 44

Speed of current = x kmph

$$\Large \therefore$$ Speed of the boat in still water = 7x kmph

$$\Large \therefore$$ Rate upstream

7x - x = 6x kmph

$$\Large \therefore \frac{Distance}{speed} = time$$

=> $$\Large \frac{4.2}{6x} = \frac{14}{60}$$

=> $$\Large 14x = 42 => x = \frac{42}{14} = 3$$

Rate downstream

= 7x + x = 8x

$$\Large 8 \times 3 = 24 \ kmph$$

Time taken in covering 17.6 km

= $$\Large \frac{17.6}{24} \ hour$$

= $$\Large (\frac{17.6 \times 60}{24} ) \ minutes$$

= 44 minutes

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