Pipes P and Q can fill a tank in 10 and 20 hours respectively. Pipe Q can empty it in 24 hours. If all the three pipes are opened together, then the tank will be filled in what time? Pick one:
A) 9 3/7 B) 5 2/7 C) 5 6/7 D) 9 3/13 E) 3
Pipe----------P---------Q--------R--------------(P+Q-R)--   Time--------10--------20-------24----------------x   *   Rate---------12--------6---------5---------------13   Work--------120------120------120--------------120   Time required to fill the tank if all the 3 pipes are open = 120/13   = 9 3/13   Ans -9 3/13
<result>D</result>
Pipes P and Q can fill a tank in 10 and 20 hours respectively. Pipe Q can empty it in 24 hours. If all the three pipes are opened together, then the tank will be filled in what time?