Multiple choice

There are 3 pipes A, B and C in a tank. Inlet pipes A and B together can fill the tank in 15 minutes while outlet pipe C can empty the full tank in 25 minutes. An outlet pipe D is also added to the tank. Now if all the pipes are opened together, the tank gets full in 50 minutes. Find the time in which pipe D alone can empty the full tank.

  1. 120 minutes

  2. 150 minutes

  3. 140 minutes

  4. 130 minutes
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

A and B together: 1/15 tank/min. C empties: 1/25 tank/min. With D added, net rate = 1/15 - 1/25 - 1/D = 1/50. Solving: 1/15 - 1/25 - 1/50 = 1/D. LCM(75): 5-3-1.5 = 0.5, so 1/D = 1/150, D = 150 min. Options A, C, and D are common errors in rate arithmetic.

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