Pipes & Cisterns · Question 21 · Medium
Pipes & Cisterns question 21
Pipe A can fill a tank in 12 hours and pipe B in 16 hours. Both are opened together on the empty tank. After how many hours should B be closed so that the tank is full exactly 9 hours after the start?
- 6 hours
- 3 hours
- 4 hours
- 5 hours
Answer and explanation
Answer: C. 4 hours
Explanation: A runs for all 9 hours and fills 9/12 = 3/4. B must fill the remaining 1/4, which takes 1/4 × 16 = 4 hours.
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