Multiple choice

Two pipes A and B can fill a tank independently in 10 hours and 15 hours respectively, while pipe C can empty it in 30 hours. All pipes are kept open for 6 hours after which pipes B and C are closed. In what time now onwards would the tank get full?

  1. 6

  2. 5

  3. 3

  4. 2

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

Combined rate with all pipes: 1/10 + 1/15 - 1/30 = 4/30 = 2/15 tank per hour. In 6 hours, tank fills 6 × 2/15 = 4/5. Remaining 1/5 is filled by A alone at rate 1/10 per hour. Time = (1/5) ÷ (1/10) = 2 hours. Option D is correct.

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