two pipes p and q can fill a cistern in 12 and 15 minutes respectively. both are opened together, but at the end of 3 minutes the first is turned off. how much longer will the cistern take to fill?

11 1/4 min

7 1/4 min

9 1/4 min

8 1/2 min

two pipes p and q can fill a cistern in 12 and 15 minutes respectively. both are opened together, but at the end of 3 minutes the first is turned off. how much longer will the cistern take to fill?

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