A cistern can be filled by a tap in 3 hours while it can be emptied by another tap in 9 hours. If both the taps are opened simultaneously, then after how much time will the cistern get filled ?	Pick:	A) 4.5 hrs	B) 5 hrs	C) 6.5 hrs	D) 7.2 hrs	E) 9.2 hrs
Net part filled in 1 hour= 1/3 -1/9= 2/9   Therefore the cistern will be filled in 9/2 hours or 4.5 hours.   4.5 hrsNSWER:4.5 hrs
<result>A</result>
A cistern can be filled by a tap in 3 hours while it can be emptied by another tap in 9 hours. If both the taps are opened simultaneously, then after how much time will the cistern get filled ?