Correct Answer: Option C
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 = ((1/4)+(1/3)) = 7/12.
B's 1 hour's work = (7/12 – 1/2)= 1/12
Therefore, B alone will take 12 hours to do the work.
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