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1. |
Two pipes A and B can separately fill a cistern in 10 and 15 minutes respectively. A person opens both the pipes together when the cistern should have been was full he finds the waste pipe open. He then closes the waste pipe and in another 4 minutes the cistern was full. In what time can the waste pipe empty the cistern when fill? |
A. | 7 min |
B. | 8 min |
C. | 9 min |
D. | 10 min |
Answer» C. 9 min | |