Q. A can do a piece of work in 4 hours, B and C can do it in 3 hours. A and C can do it in 2 hours. How long will B alone take to do it?
Answer: 12 hours
Notes: A's one hour's work $latex = \frac{1}{4}&s=1$ (B + C)'s one hour's work $latex = \frac{1}{3}&s=1$ (A + C)'s one hour's work $latex = \frac{1}{2}&s=1$ ∴ C's one hour's work $latex = \frac{1}{2}-\frac{1}{4} = \frac{2-1}{4} = \frac{1}{4}&s=1$ B's one hour's work $latex = \frac{1}{3}-\frac{1}{4} = \frac{4-3}{12} = \frac{1}{12}&s=1$ Hence B alone can do the work in 12 hours, so option [D] is correct answer

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