Multiple choice

Time taken by a boat to cover a certain distance in upstream is twice the time taken to cover the same distance in downstream. If speed of the stream is 6 km/hr., what is the speed of boat in still water?

  1. 12 km/hr.

  2. 18 km/hr.

  3. 24 km/hr.

  4. 30 km/hr.
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Let boat speed = b, stream speed = 6 km/h. Downstream speed = b + 6, upstream = b - 6. Time upstream = 2 × time downstream, so distance/(b-6) = 2 × distance/(b+6). Cancel distance: b + 6 = 2b - 12, giving b = 18 km/h. Option B is correct.

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