A water tank is one-third 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 answer:
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 = 1/3   part emptied by (A+B) in 1 minute=(1/6-1/10)=1/15   so, the tank will be emptied in 5 min   Answer: 5 min.to empty
<result>C</result>
A water tank is one-third 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?