Some question: A pipe can fill a cistern in 20 minutes whereas the cistern when fill can be emptied by a leak in 60 minutes. When both pipes are opened, find when the cistern will be full?\nOptions:\n(A) 17 minutes\n(B) 87 minutes\n(C) 30 minutes\n(D) 27 minutes\n(E) 11 minutes
Some stream of consciousness:
User
1/20 - 1/60 = 1/30\n30 minutes The answer: (C).
Assistant