A cistern can be filled by a tap in 3 hours while it can be emptied by another tap in 6 hours. If both the taps are opened simultaneously, then after how much time will the cistern get filled?	Select the correct option:  A) 5.2 hrs  B) 2.9 hrs  C) 1.9 hrs  D) 6 hrs  E) 5 hrs

Rationale: "net part filled in 1 hour = ( 1 / 3 - 1 / 6 ) = 1 / 6 the cistern will be filled in 6 / 1 hrs i . e . , 6 hrs . answer : d"
Answer: D