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?

(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.