hard · GMAT Quant
Pipes A and B can fill an empty cistern in 12 hours and 20 hours, respectively. They are opened together on an empty cistern. After 4 hours, a drain is also opened; the drain alone would empty a full cistern in 15 hours, and all three then run until the cistern is full.
What is the total time from the start until the cistern is completely full?
- 11 hours
- 6.33 hours
- 15 hours
- 7 hours
- 7.5 hours
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