Three pipes A, B and C can fill a tank in 6 hours, 9 hours

Three pipes A, B and C can fill a tank in 6 hours, 9 hours and 12 hours respectively. B and C are opened for half an hour, then A is also opened. The time taken by the three pipes together to fill the remaining part of the tank is

Given in question ,

Part of the tank filled by B and C in half an hour =	1		1	+	1
	2		9		12

Part of the tank filled by B and C in half an hour =	1		4 + 3		=	7
	2		36			72

Remaining part = 1 -	7	=	72 - 7	=	65
	72		72		72

Part of tank filled by three pipes in an hour =	1	+	1	+	1
	6		9		12

Part of tank filled by three pipes in an hour =	6 + 4 + 3	=	13
	36		36

∴ Time to fill remaining part =	65	×	36	=	5	= 2	1	hours.
	72		13		2		2