Two pipes A and B can fill a tank in 20 and 30 minutes respectively. If both the pipes are used together, then how long will it take to fill the tank?	Choose one:
A) 12
B) 55
C) 77
D) 82
E) 22
Part filled by A in 1 min. = 1/20   Part filled by B in 1 min. = 1/30   part filled by (A + B) in 1 min. = 1/20 + 1/30 = 1/12.   Both the pipes can fill the tank in 12 minutes.   12nswer: 12
<result>A</result>
Two pipes A and B can fill a tank in 20 and 30 minutes respectively. If both the pipes are used together, then how long will it take to fill the tank?