Multiple choice

In a river flowing at 2 km/hr, a boat travels 30 km upstream and then returns downstream to the starting point. If its speed in still water is 6 km/hr, then find the time taken to cover the whole journey.

  1. 22.25 hours

  2. 11.25 hours

  3. 9.5 hours

  4. 10 hours

  5. None of these
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Upstream speed = 6 - 2 = 4 km/hr. Downstream speed = 6 + 2 = 8 km/hr. Time upstream = 30/4 = 7.5 hours. Time downstream = 30/8 = 3.75 hours. Total time = 7.5 + 3.75 = 11.25 hours.

AI explanation

The speed of the boat upstream is its speed in still water minus the speed of the stream, which is 6 - 2 = 4 km/hr. The downstream speed is 6 + 2 = 8 km/hr. The time taken to travel 30 km upstream is 30 divided by 4, equaling 7.5 hours. The time taken to travel 30 km downstream is 30 divided by 8, equaling 3.75 hours. The total time for the whole journey is 7.5 + 3.75, which is 11.25 hours.

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