Two pipes A and B can fill a tank in 15 minutes and 20 minutes respectively. Both the pipes are opened together but after 4 minutes, pipe A is turned off. What is the total time required to fill the tank?
Choose the correct choice from the following choices:
A) 10 min. 20 sec.	B) 11 min. 45 sec.	C) 12 min. 30 sec.	D) 14 min. 40 sec.	E) 15 min. 40 sec.
Take LCM of 15 and 20 and get the total capacity of tank as 60 .   Then A will fill 4li in 1 min and B will fill 3 li in 1 min so total will be 7 . A left after 4 min so they worked together for 4 min so   7*4= 
<gadget id="calculator">  7*4</gadget>
<output>28</output>
28 . now subtract it from 60.(60-38=32). This will be filled by b so time taken would be..10 min 20 sec.   10 min. 20 sec.NSWER:10 min. 20 sec.
<result>A</result>
Two pipes A and B can fill a tank in 15 minutes and 20 minutes respectively. Both the pipes are opened together but after 4 minutes, pipe A is turned off. What is the total time required to fill the tank?