Multiple choice

A boat can travel 20 km downstream in 1 hour and the same distance upstream in 2 hours. What is the ratio of the speed of boat to that of the current?

  1. 5 : 2

  2. 3 : 1

  3. 3 : 2

  4. 4 : 1
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B Correct answer
Explanation

The downstream speed of the boat is 20 km/h and the upstream speed is 10 km/h. The speed of the boat in still water is the average of these two speeds, which is 15 km/h, and the speed of the current is half their difference, which is 5 km/h. The ratio of the speed of the boat to the speed of the current is 15:5, which simplifies to 3:1.

AI explanation

The downstream speed is 20 divided by 1, which equals 20 kmph, and the upstream speed is 20 divided by 2, which equals 10 kmph. Using the boat and stream formula, the speed of the boat in still water is (20 plus 10) divided by 2, which is 15 kmph, and the speed of the current is (20 minus 10) divided by 2, which is 5 kmph. The required ratio of the speed of the boat to the speed of the current is 15 to 5, which equals 3 to 1.

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