Pipes & Cisterns · Question 12 · Hard
Pipes & Cisterns question 12
Pipe A fills a tank in 6 hours and pipe B in 9 hours. They are opened alternately for one hour each, starting with A. How long will it take to fill the empty tank?
- 7 hours
- 8 hours
- 7 1/3 hours
- 7 1/2 hours
Answer and explanation
Answer: A. 7 hours
Explanation: Each 2-hour cycle fills 1/6 + 1/9 = 5/18. After 3 cycles (6 hours) 15/18 is full. In the 7th hour A adds 1/6 = 3/18, which fills the tank exactly, so 7 hours.
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