A pipe can fill a cistern in 18 minutes whereas the cistern when fill can be emptied by a leak in 36 minutes. When both pipes are opened, find when the cistern will be full?
Options:
(A) 17
(B) 36
(C) 70
(D) 13
(E) 12 Stream of consciousness first, then make a decision:
1/18 - 1/36 = 1/36
36 minutes
Thus, the answer is (B).