There are 12 pipes attached to a tank Some of them are fill pipes and some are drain pipes. Each of the fill pipes an ill the tank in 12 hours, while each of the drain pipes will take 24 hours to drain full tank completely. If all the pipes are kept open when the tank was empty It takes 2 hours for the tank to overflow. How many of these pipes are drain pipes

Options

A. 6
B. 11
C. 4
D. 7

Answer

C