question_answer

Three pipes P, Q and R connected to a cistern. The first pipe (i.e) P can fill 1/2 part of the tank in one hour, second pipe, Q can fill 1/3 part of the cistern in one hour. R is connected to empty the cistern. After opening all the three pipes in a cistern which is 7/12 part filled. Then how much time required to empty the cistern completely?

A) 2 hours

B) 3 hours

C) 4 hours

D) 5 hours

E) None of the Above