Multiple choice general knowledge math & puzzles

A large water tank has two inlet pipes (a large one and a small one) and one outlet pipe. It takes 2 hours to fill the tank with the large inlet pipe. On the other hand, it takes 4 hours to fill the tank with the small inlet pipe. The outlet pipe allows the full tank to be emptied in 6 hours. What fraction of the tank (initially empty) will be filled in 0.86 hours if all three pipes are in operation?

  1. 0.25

  2. 0.45

  3. 0.5

  4. 0.55

  5. 0.75
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

Large inlet fills 1/2 tank per hour, small inlet fills 1/4 tank per hour, outlet empties 1/6 tank per hour. Net rate = 1/2 + 1/4 - 1/6 = 6/12 + 3/12 - 2/12 = 7/12 tank per hour. In 0.86 hours: 7/12 * 0.86 = 0.5017, approximately 0.5.

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