Multiple choice

Aleena rows a boat for 350 m in 475 seconds against the stream. She covers the same distance along the stream in 2 min and 30 seconds. Her rowing speed in still water is

  1. 2.4 km/h

  2. 2.5 km/h

  3. 3 km/h

  4. 5.5km/h

  5. 4.1 km/h
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

Against stream: speed = 350m / 475s = 350/475 m/s = 14/19 m/s = 2.65 km/h. With stream: speed = 350m / 150s = 350/150 m/s = 7/3 m/s = 8.4 km/h. Boat speed = (8.4 + 2.65) / 2 = 5.525 km/h.

AI explanation

The speed against the stream is 350 m divided by 475 seconds, which equals 14/19 m/s. The speed along the stream is 350 m divided by 150 seconds, which equals 7/3 m/s. Using the still water speed formula of half the sum of the upstream and downstream speeds, we calculate ((14/19) + (7/3)) divided by 2 to get 175/114 m/s. Multiplying by 18/5 to convert to km/h gives exactly 5.5 km/h, so the correct answer is 5.5km/h.

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