Two pipes A and B can fill a tank in 15 min and 27 min respectively. Both the pipes are opened together but after 4 min, pipe A is turned off. What is the total time required to fill the tank?  Choose the correct answer:	A) 14 min 19 sec	B) 14 min 42 sec	C) 18 min 24 sec	D) 14 min 40 sec	E) 14 min 10 sec
:   Part filled in 4 minutes = 4(1/15 + 1/20) = 7/15   Remaining part = 1 - 7/15 = 8/15   Part filled by B in 1 minute = 1/27   1/27 : 8/15 :: 1 ; x   x = 8/15 * 1 * 27 = 14 2/5 min = 14 min 24 sec.   The tank will be full in (4 min. + 14 min. 24 sec) = 18 min 24 sec.Answer: 18 min 24 sec
<result>C</result>
Two pipes A and B can fill a tank in 15 min and 27 min respectively. Both the pipes are opened together but after 4 min, pipe A is turned off. What is the total time required to fill the tank?