A and B alone can do a work in 12 and 18 days respectively. A, B and C together can do the same work in 6 days. In how many days can C do the work alone?
A24
B36
C30
D48
Correct answer: B
Explanation
Work of A and B in 1 day = 1/12 + 1/18 = 5/36. C's one-day work = 1/6 – 5/36 = 1/36, so C alone takes 36 days.