Multiple choice

DIRECTION for the question: Solve thefollowing question and mark the best possibleoption.Two pipes A and B can fill a tank in 15 hoursand 20 hours respectively while a third pipe Ccan empty the full tank in 25 hours. All the threepipes are opened in the beginning. After 10hours, C is closed. In how much time will thetank be full?

  1. 13HRS

  2. 16HRS

  3. 12HRS

  4. 18HRS

  5. 20HRS
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

Work rates: A=1/15, B=1/20, C=-1/25. Combined rate = (20+15-12)/300 = 23/300. In 10 hours, work done = 230/300 = 23/30. Remaining work = 7/30. After C closes, rate = 1/15 + 1/20 = 7/60. Time to finish = (7/30) / (7/60) = 2 hours. Total time = 10 + 2 = 12 hours.

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