Multiple choice

A tank can be filled by two pipes A and B separately in 3 hours and 3 hours 45 minutes respectively, A third pipe C can empty the full tank in 1 hour, when the tank was exactly half-filled, all the three pipes are opened. The tank will become empty in

  1. 1 hours 15 min

  2. 2 hours 30 min

  3. 3 hours 15 min

  4. 4 hours 10 min
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

Rate A = 1/3, Rate B = 1/(3.75) = 1/(15/4) = 4/15. Rate C = -1. Net rate = 1/3 + 4/15 - 1 = 5/15 + 4/15 - 15/15 = -6/15 = -2/5. The tank is half-filled (1/2). Time to empty = (1/2) / (2/5) = 5/4 hours = 1 hour 15 minutes.

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