A water tank is two-fifth full. Pipe A can fill a tank in 10 minutes and pipe B can empty it in 5 minutes. If both the pipes are open, how long will it take to empty or fill the tank completely?	Select the correct option:
A) 4 min. to empty	B) 6 min. to full	C) 9 min. to empty	D) 9 min. to full	E) 8 min. to full
Clearly, pipe B is faster than pipe A and so, the tank will be emptied.   Part to be emptied = 2/5   Part emptied by (A + B) in 1 minute = (1/5 - 1/10) = 1/10   1/10 : 2/5 :: 1 : x   x = (2/5 * 1 * 10)= 
<gadget id="calculator">(2/5 * 1 * 10)</gadget>
<output>4</output>
4 min.   So, the tank will be emptied in 4 min.   4 min. to emptyNSWER:4 min. to empty
<result>A</result>
A water tank is two-fifth full. Pipe A can fill a tank in 10 minutes and pipe B can empty it in 5 minutes. If both the pipes are open, how long will it take to empty or fill the tank completely?