Multiple choice

A boat takes 5 hours to travel a distance of 30 km against the stream and 10 hours to travel 100 km with the stream. The ratio of the speed of the boat in still water to the speed of the stream is

  1. 1 : 4

  2. 4 : 1

  3. 2 : 1

  4. 1 : 2
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Against stream: v - u = 30/5 = 6. With stream: v + u = 100/10 = 10. Adding: 2v = 16, v = 8. Subtracting: 2u = 4, u = 2. Ratio v:u = 8:2 = 4:1.

AI explanation

The speed of the boat against the stream is 30 km divided by 5 hours, which equals 6 km/hr, and the speed with the stream is 100 km divided by 10 hours, which equals 10 km/hr. Using the still water speed formula, the boat's speed is (10 + 6) divided by 2, equaling 8 km/hr, and the stream's speed is (10 - 6) divided by 2, equaling 2 km/hr. Thus, the required ratio of the speed of the boat in still water to the speed of the stream is 8 to 2, or 4 : 1.

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