Multiple choice

A motorboat can travel at a speed of 9 km/hr. It takes twice the time to travel upstream than to travel downstream. Find out the rate of flow of the stream.

  1. 3 km/hr

  2. 5 km/hr

  3. 10 km/hr

  4. 12 km/hr

  5. 14 km/hr
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A Correct answer
Explanation

Let boat speed = 9, stream speed = s. Downstream speed = 9+s, Upstream = 9-s. Time = Distance / Speed. 1/(9-s) = 2 * 1/(9+s). 9+s = 18-2s. 3s = 9. s = 3.

AI explanation

Since the boat takes twice the time to travel upstream compared to downstream, its upstream speed is half of its downstream speed. Using the given still water speed of 9 km/hr, downstream speed equals 9 plus the stream rate and upstream speed equals 9 minus the stream rate, leading to the equation 9 plus x equals 2 times (9 minus x). Solving this gives 3x equals 9, so the rate of flow of the stream is 3 km/hr. The result is 3 km/hr.

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