Multiple choice

The speed of a boat in still water is 9.5 kmph while that of current is 2.5 kmph. If the boat takes 285 minutes in rowing from point A to B and coming back to point A, what is the distance between point A and B?

  1. 24 km

  2. 21 km

  3. 8.5 km

  4. 15 km
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Downstream speed = 9.5 + 2.5 = 12 kmph. Upstream speed = 9.5 - 2.5 = 7 kmph. Total time = 285 minutes = 4.75 hours = 19/4 hours. Distance = d, so d/12 + d/7 = 19/4. Solving: 7d + 12d = (19 × 21)/4, giving d = 21 km.

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