Multiple choice

Three pipes A , B and C can fill a cistern in 6 hours. After working at it together for 2 hours C is closed and A and B fill it in 7 hours more. How many hours will C alone take to fill the cistern?

  1. 10 hours

  2. 14 hours

  3. 16 hours

  4. None of these
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

In 2 hours, all three pipes fill 2/6 = 1/3 of the cistern. The remaining 2/3 is filled by A and B in 7 hours, so their combined rate is (2/3)/7 = 2/21 per hour. C's rate equals the total rate (1/6) minus A and B's rate (2/21), which simplifies to 1/14 per hour. This means C alone fills the cistern in 14 hours.

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