(a) 8 hours
(b) 10 hours
(c) 12 hours
(d) 24 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 = (1/4 + 1/3) = 7/12.
B’s 1 hour’s work = (7/12 – 1/2) = 1/12.
B alone will take 12 hours to do the work.