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 the correct answer:
A) 6 hours  B) 8 hours  C) 3 hours  D) 9 hours  E) 1 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?