Two pipes A and B can fill a cistern in 37 minutes and 45 minutes respectively. Both pipes are opened. The cistern will be filled in just half an hour, if the B is turned off after? Choose the correct choice from the following options: A) 7 B) 9 C) 11 D) 13 E) 15
Let B be turned off after x minutes. Then,   Part filled by (A + B) in x min. + Part filled by A in (30 -x) min. = 1.   x 2	+	1 + (30 - x).	2	= 1   75	45	75   11x	+	(60 -2x)	= 1   225	75   11x + 180 - 6x = 225.   x = 9.   9)
<result>B</result>
Two pipes A and B can fill a cistern in 37 minutes and 45 minutes respectively. Both pipes are opened. The cistern will be filled in just half an hour, if the B is turned off after?