Multiple choice

Pipe A and Pipe B can fill a tank in 10 hours and 15 hours respectively. When a third pipe C which work as an outlet pipe is also open then the tank can be filled in 18 hours. The outlet pipe can empty a full tank in :

  1. 12

  2. 8

  3. 9

  4. 14

  5. None of these
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

A fills in 10 hrs → rate = 1/10 tank/hr. B fills in 15 hrs → rate = 1/15 tank/hr. C empties in x hrs → rate = -1/x tank/hr. Combined rate when all open: 1/10 + 1/15 - 1/x = 1/18. Solving: (3+2)/30 - 1/x = 1/18 → 5/30 - 1/x = 1/18 → 1/6 - 1/18 = 1/x → (3-1)/18 = 1/x → 2/18 = 1/x → x = 9 hrs.

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