Two pipes can fill a tank in 10 hours & 12 hours respectively. While 3rd pipe empties the full tank n 20 hours. If all the three pipes operate simultaneously,in how much time will the tank be filled?	Select the correct option
A) 6 hrs 43 min	B) 2 hrs 25 min	C) 7 hrs 30 min	D) 6 hrs 32 min	E) 7 hrs 10 min
tank filled in 1 hr = 1/10 + 1/12 - 1/20 = 8/60 = 2/15 part   so full tank is filled in 15/2 hrs = 7 hr 30 min..   ANSWER:7 hrs 30 min
<result>C</result>
Two pipes can fill a tank in 10 hours & 12 hours respectively. While 3rd pipe empties the full tank n 20 hours. If all the three pipes operate simultaneously,in how much time will the tank be filled?