Q. A motorboat in still water traveles at a speed of 36 kmph. It goes 56 km upstream in 1 hour 45 minutes. The time taken by it to cover the same distance down the stream will be :
Answer: 1 Hours 24 Minutes
Notes: Speed of the motorboat upstream = $latex \frac{56 km}{1\frac{3}{4}hours} = \frac{56\times 4}{7} = 32 kmph&s=2$ Let the speed of the current be x kmph ∴ 36 - x = 32 $latex => x = 36 - 32 = 4 kmph$ Speed of motor boat downstream = 36 + 4 = 40 kmph ∴ Time taken to cover 56 km at 40 kmph = $latex \frac{56}{40} = \frac{7}{5}hours&s=1$ or 1 hours 24 minutes. Hence option [B] is the right answer.

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