A Cistern is filled by pipe A in 9 hrs and the full Cistern can be leaked out by an exhaust pipe B in 12 hrs. If both the pipes are opened in what time the Cistern is full?
Choose the correct answer.
A) 28 hrs
B) 24 hrs
C) 36 hrs
D) 32 hrs
E) 34 hrs
Explanation:   Pipe A can fill 1/9 of the cistern in 1 hour.   Pipe B can empty 1/12 of the cistern in 1 hour   Both Pipe A and B together can effectively fill 1/9 − 1/12 = 1/36 of the cistern in 1 hour   i.e, the cistern will be full in 36 hrs.   Answer: Option 36 hrs
<result>C</result>
A Cistern is filled by pipe A in 9 hrs and the full Cistern can be leaked out by an exhaust pipe B in 12 hrs. If both the pipes are opened in what time the Cistern is full?