If the first pipe takes 60 mins to fill a tank and second takes 90 mins to empty it, then in how much time will the tank be full, if the second pipe is opened 30 mins earlier than the first pipe and the tank is empty at first?
Explanation:
The time required to fill the tank is 180 minutes
1/60 - 1/90 = 1/180
The fact that the second pipe was opened earlier makes no difference as the tank is empty.
Hence, option (b).
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