A cistern can be filled by a tap in 2 hours while it can be emptied by another tap in 4hours. If both the taps are opened simultaneously then after how much time will the cistern get filled?	Pick one:
A) 2hr
B) 5hr
C) 7hr
D) 1hr
E) 4hr
Net part filled in 1 hour 1/2 - 1/4 = 1/4   The cistern will be filled in 4 hr   Answer is 4hr
<result>E</result>
A cistern can be filled by a tap in 2 hours while it can be emptied by another tap in 4hours. If both the taps are opened simultaneously then after how much time will the cistern get filled?