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?  Choose one
A) 2 hours	B) 9 hours	C) 3 hours	D) 7 hours	E) 2 hours
Part filled by A + B + C in 1 hour   = 1/5 + 1/10 + 1/30   = 1/3   All the three pipes together will fill the tank in 3 hours.   Answer:3 hours
<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?