Two pipes A and B can fill a tank in 4 and 12 minutes respectively. If both the pipes are used together, then how long will it take to fill the tank?  Pick one:	A) 12	B) 3	C) 6	D) 9	E) 10
Part filled by A in 1 min. = 14   Part filled by B in 1 min. = 1/12   part filled by (A + B) in 1 min. = 1/4+ 1/12 = 1/3.   Both the pipes can fill the tank in 3 minutes.   Answer: 3
<result>B</result>
Two pipes A and B can fill a tank in 4 and 12 minutes respectively. If both the pipes are used together, then how long will it take to fill the tank?