A pipe can fill a cistern in 7 minutes whereas the cistern when fill can be emptied by a leak in 14 minutes. When both pipes are opened, find when the cistern will be full?	Select:
A) 17
B) 16
C) 70
D) 14
E) 12
1/7 - 1/14 = 1/14   14 minutes   Answer: 14
<result>D</result>
A pipe can fill a cistern in 7 minutes whereas the cistern when fill can be emptied by a leak in 14 minutes. When both pipes are opened, find when the cistern will be full?