A and B can do a piece of work in 18 days. B and C in 24 days, C and A in 36 days. Find the time in which A, B and C working together can finish the work.

(A+ B )' s 1 day ' s work = 1/18
(B +C )'s 1 day ' s work = 1/24
(C + A) 's 1 day 's work = 1/36
From Eqs. (i), (ii) and (iii), we get
2(A + B + C)' s 1 day 's work = 1/18 + 1/24 + 1/36
(A + B + C)'s 1 day's work = (4 + 3 + 2)/(72 x 2)
= 9/(72 x 2) = 1/16
∴ (A + B + C) can complete the work in 16 days