A pipe can fill a cistern in 20 minutes whereas the cistern when fill can be emptied by a leak in 28 minutes. When both pipes are opened, find when the cistern will be full?\nOptions:\n(A) 22 minutes\n(B) 88 minutes\n(C) 70 minutes\n(D) 77 minutes\n(E) 48 minutes Hmmm, my stream of consciousness:
User
1/20 - 1/28 = 1/70\n70 minutes So, the answer is (C).
Assistant