A pipe can fill a cistern in 20 minutes whereas the cistern when fill can be emptied by a leak in 45 minutes. When both pipes are opened, find when the cistern will be full?\nOptions:\n(A) 17 minutes\n(B) 87 minutes\n(C) 36 minutes\n(D) 27 minutes\n(E) 11 minutes OK. Let's think. Some random thoughts first:
User
1/20 - 1/45 = 1/36\n36 minutes The answer: (C).
Assistant