Multiple choice general knowledge math & puzzles

Pipe A can fill a tank in 36 hours and pipe B can empty it in 45hours. If both the pipes are opened simultaneously, how much time will be taken to fill the tank?

  1. 90 hrs

  2. 100 hrs

  3. 150 hrs

  4. 180 hrs
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

Pipe A fills at 1/36 of the tank per hour and pipe B empties at 1/45 per hour. The net fill rate is 1/36 - 1/45 = (5-4)/180 = 1/180 per hour, so the tank fills in 180 hours. Options 90, 100, and 150 hrs ignore the net rate.

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