Pipe A can fill a tank in 5 hours, pipe B in 10 hours and pipe C in 30 hours. If all the pipes are open,in how many hours will the tank be filled ? Pick
A) 2  B) 2.5  C) 3  D) 3.5  E) 4
1/5+1/10+1/30=10/30=1/3. soo 3 hrs   ANSWER:3
<result>C</result>
Pipe A can fill a tank in 5 hours, pipe B in 10 hours and pipe C in 30 hours. If all the pipes are open,in how many hours will the tank be filled ?