Two pipes A and B can fill a tank in 12 and 24 minutes respectively. If both the pipes are used together, then how long will it take to fill the tank?
Choose one:
A) 9 B) 8 C) 6 D) 4 E) 10
Part filled by pipe A in 1 minute =1/12   =1/12   Part filled by pipe 8 in 1 minute =1/24   =1/24   Part filled by pipe A and pipe 8 in 1 minute=   1/12 + 1/24 =1/8   =1/12+1/24=1/8   i.e., both the pipe together can fill the tank in 8 minutes.
<result>B</result>
Two pipes A and B can fill a tank in 12 and 24 minutes respectively. If both the pipes are used together, then how long will it take to fill the tank?