Multiple choice

Two boats are tied at two points, 10 km apart, along a river, one facing upstream and the other facing downstream. The river is flowing at a rate of 3 kmph. The two boats start moving towards each other. The speeds of the boats going downstream and upstream are 12 kmph and 13 kmph, respectively. If they start moving towards each other at the same time, then after how much time will they cross each other?

  1. 12 min

  2. 18 min

  3. 24 min

  4. 28 min

  5. 32 min
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

The boats move towards each other. Downstream speed = 12 kmph, Upstream speed = 13 kmph. Relative speed = 12 + 13 = 25 kmph. Time = Distance / Relative Speed = 10 km / 25 kmph = 0.4 hours = 24 minutes.

AI explanation

The speed of the boat going downstream relative to the ground is its given speed plus the river speed, which is 12 + 3 = 15 kmph. The speed of the other boat going upstream relative to the ground is its given speed minus the river speed, which is 13 - 3 = 10 kmph. Since they are moving towards each other, their relative speed is 15 + 10 = 25 kmph. Using the formula time equals distance divided by speed, the time to cross each other is 10/25 hours, which equals 2/5 hours or 24 minutes.

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