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?
Select the correct option:
A) 17 minutes B) 87 minutes C) 36 minutes D) 27 minutes E) 11 minutes
1/20 - 1/45 = 1/36   36 minutes   Answer:36 minutes
<result>C</result>
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?