A can do a piece of work in 4 hours; B and C together can do it in 3 hours, while A and C together can do it in 2 hours. How long will B alone take to do it?

8 hours
10 hours
12 hours
24 hours

Correct Answer: 12 hours

Explanation:

A's 1 hour's work =	1	;
	4

(B + C)'s 1 hour's work =	1	;
	3

(A + C)'s 1 hour's work =	1	.
	2

(A + B + C)'s 1 hour's work =	❨	1	+	1	❩	=	7	.
		4		3			12

B's 1 hour's work =	❨	7	-	1	❩	=	1	.
		12		2			12

∴ B alone will take 12 hours to do the work.

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