A water tank is two-fifth full. Pipe A can fill a tank in 10 minutes and pipe B can empty in 6 minutes. If both the pipes are open, how long will it take to empty or fill the tank completely ?	Select.
A) 7 min to empty	B) 5 min to full	C) 4 min to full	D) 2 min to empty	E) 6 min to empty
1/6-1/10 == 1/15   1/15:2/5::1 : x    2/5*15= 
<gadget id="calculator"> 2/5*15</gadget>
<output>6</output>
6 min   ANSW6 min to emptyR 6 min to empty
<result>E</result>
A water tank is two-fifth full. Pipe A can fill a tank in 10 minutes and pipe B can empty in 6 minutes. If both the pipes are open, how long will it take to empty or fill the tank completely ?