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Math
Two pipes A and B can fill a tank in 15 minutes and 20 minutes respectively. Both the pipes are opended together but after 4 minutes, pipe A is turned off. What is the total time required to fill the tank?
A) 10 min 20 sec
B) 11 min 45 sec
C) 12 min 30 sec
D) 14 min 40 sec
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