Pipe A can fill a tank in 7 hours, pipe B in 14 hours and pipe C in 42 hours. If all the pipes are open,in how many hours will the tank be filled ?
Pick.
A) 4	B) 4.2	C) 4.5	D) 4.3	E) 4.1
1/7+1/14+1/42=10/42=1/4.2. so 4.2 hrs   ANSWER:4.2
<result>B</result>
Pipe A can fill a tank in 7 hours, pipe B in 14 hours and pipe C in 42 hours. If all the pipes are open,in how many hours will the tank be filled ?