Multiple choice

The speed of a boat while moving a particular distance downstream is 25 m/s. Its speed in still water is 18 m/s. What is the ratio of time taken by the same boat to cover an equal distance in upstream and then, in downstream direction?

  1. 25 : 11

  2. 11 : 25

  3. 64 : 22

  4. 22 : 64

  5. 64 : 11
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A Correct answer
Explanation

Downstream speed = 25 m/s. Still water speed = 18 m/s. Stream speed = 25 - 18 = 7 m/s. Upstream speed = 18 - 7 = 11 m/s. Time taken for distance D: Upstream time = D/11, Downstream time = D/25. Ratio of Upstream time to Downstream time = (D/11) / (D/25) = 25/11.

AI explanation

The speed of the stream is the difference between the downstream speed and the still water speed, which is 25 m/s - 18 m/s = 7 m/s. The upstream speed is found by subtracting the stream speed from the still water speed, giving 18 m/s - 7 m/s = 11 m/s. Since time is inversely proportional to speed for a constant distance, the ratio of the time taken upstream to downstream is the inverse of their speeds, yielding 25 : 11.

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