Three taps A,B and C together can fill an empty cistern

Three taps A,B and C together can fill an empty cistern in 10 minutes. The tap A alone can fill it in 30 minutes and the tap B alone in 40 minutes.How long will the tap C alone take to fill it ?

On the basis of given details in question ,

Part of the cistern filled by taps A, B and C in 1 minute =	1
	10

Part of the cistern filled by taps A and B in 1 minute =	1	+	1	=	4 + 3	=	7
	30		40		120		120

∴ Part of the cistern filled by tap C in 1 minute =	1	-	7	=	12 - 7	=	5	=	1
	10		120		120		120		24

∴ Tap C will fill the cistern in 24 minutes.