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?	Choose the correct choice from the following choices.
A) 17 B) 36 C) 70 D) 13 E) 12
1/18 - 1/36 = 1/36   36 minutes   Answer: 36
<result>B</result>
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?