Pipes & Cisterns · Question 25 · Medium
Pipes & Cisterns question 25
An inlet can fill a tank in 9 hours and an outlet can empty it in 12 hours. The tank is empty when the inlet is opened at 8 AM; the outlet is opened at 11 AM. At what time will the tank be full?
- 2 AM the next day
- 11 AM the next day
- 5 PM the same day
- 8 PM the same day
Answer and explanation
Answer: B. 11 AM the next day
Explanation: By 11 AM the inlet fills 3/9 = 1/3. After that the net rate is 1/9 − 1/12 = 1/36 per hour, so the remaining 2/3 takes 24 hours, i.e. till 11 AM the next day.
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