A water tank is three-fifth full.Pipe A can fill a tank in 10 minutes and pipe B can empty it in 6 minutes.If both the pipes are open,how long will it take to empty or fill the tank completely? Choose the correct choice from the following choices:
A) 6 min.to empty  B) 9 min.to empty  C) 5 min.to empty  D) 4 min.to empty  E) 7 min.to empty
Explanation:   Clearly,pipe B is faster than pipe A and so,the tank will be emptied.   part to be emptied = 3/5   part emptied by (A+9 min.to empty) in 1 minute=(1/6-1/10)=1/15   so, the tank will be emptied in 9 min   Answer: 9 min.to empty
<result>B</result>
A water tank is three-fifth full.Pipe A can fill a tank in 10 minutes and pipe B can empty it in 6 minutes.If both the pipes are open,how long will it take to empty or fill the tank completely?