Question 97

Two water pipes A and B can fill an empty tank in 8 and 12 hrs. respectively and tap at, the bottom of the tank can empty the full tank in 9 hrs. If tap C is opened two hours after the pipes A and B are opened, then the total time (in hrs.) taken to fill the tank is

Solution

Let the capacity of the tank be 72 liters
Hence, A = 9 liters/hour, B = 6 liters/hour, C = -8 liters/hour.

Now, tank filled by A and B in the first 2 hours = 30 liters. 
Tank capacity remaining = 42 liters
After this C is opened, net filling capacity drops to 7 liters/hour
Hence, the time taken to fill remaining tank = 42/7 = 6 hours
Hence, total time taken = 2+6 = 8 hours


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