Two pipes can fill a tank in 5 hours and 10 hours. While the 3rd pipe empties the full tank in 10hours. If all the 3 pipes are open in how much time will the tank be filled?  Options
A) 6hr
B) 8hr
C) 2hr
D) 1hr
E) 5hr
Net part filled in 1 hour = 1/5 + 1/10 - 1/10 = 1/5   The tank will be full in 5 hr   Answer is 5hr
<result>E</result>
Two pipes can fill a tank in 5 hours and 10 hours. While the 3rd pipe empties the full tank in 10hours. If all the 3 pipes are open in how much time will the tank be filled?