question_answer

A tank can be filled by two pipes in 20 minutes and 30 minutes respectively. When the tank was empty, the two pipes were open. After some time, the first pipe was stopped and the tank was filled in 18 minutes. After how much time of the starting was the first pipe stopped?

A)  5 minutes                     

B)  8 minutes

C)  10 minutes                   

D)  12 minutes

E)  None of these