Two pipes A and B can fill a tank in 6 and 12 minutes respectively. If both the pipes are used together, then how long will it take to fill the tank?
Choices
A) 4  B) 6  C) 8  D) 10  E) 12
Part filled by A in 1 min. = 1/6   Part filled by B in 1 min. = 1/12   part filled by (A + B) in 1 min. = 1/6 + 1/12 = 1/4.   Both the pipes can fill the tank in 4 minutes.   4nswer: 4
<result>A</result>
Two pipes A and B can fill a tank in 6 and 12 minutes respectively. If both the pipes are used together, then how long will it take to fill the tank?