Multiple choice

The speed of a motorboat is to that of the current of water as $36 : 5$. The boat goes along with the current in $5$ hours $10$ min. It will come back in

  1. $5$ hours $50$ min
  2. $6$ hours
  3. $6$ hours $50$ min
  4. $12$ hours $10$ min
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

Let boat speed = 36x, current = 5x. Downstream speed = 41x, upstream = 31x. Time downstream = 5h 10m = 310 min. Distance = 41x * 310. Time upstream = Distance / 31x = (41x * 310) / 31x = 41 * 10 = 410 min. 410 min = 6 hours 50 min.

AI explanation

Let the speed of the motorboat be 36x and the speed of the current be 5x, making the downstream speed 41x and the upstream speed 31x. The distance covered downstream is speed multiplied by time, giving 41x multiplied by 5 and one-sixth hours, which equals 422.5x. The time to return upstream is the distance divided by the upstream speed, giving 422.5x divided by 31x, which equals 415 divided by 124 hours. Converting this improper fraction to a mixed number gives 6 hours and 50 minutes.

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