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) 76 minutes\n(B) 29 minutes\n(C) 70 minutes\n(D) 17 minutes\n(E) 98 minutes Stream of consciousness first, then make a decision:
User
1/20 - 1/28 = 1/70\n70 minutes
Thus, the answer is (C).
Assistant