A and B can do a piece of work in 18 days; B and C can do it in 24 days; A and C can do it in 36 days. In how many days can they do it all working together?

16

Following chart will be obtained with the help of LCM method:

Efficiency of A + B = 4

Efficiency of B + C = 3

Efficiency of A + C = 2

Adding all the equations:

Efficiency of 2(A + B + C) = 4 + 3 + 2

Efficiency of A + B + C = 9/2

Thus, total days required when all work together =  \(\frac{72}{9}\) x 2 = 16 days