A and B can do a work in 8 days, B and C can do the same work in 12 days. A, B and C together can finish it in 6 days. A and C together will do it in ?

Answer: Option C

L.C.M. of Total Work = 24
One day work of A + B = $$\frac{24}{8}$$ = 3 unit/day
One day work of B + C = $$\frac{24}{12}$$ = 2 unit/day
One day work of A + B + C = $$\frac{24}{6}$$ = 4 unit/day
$$\begin{array}{rl}& \text{Efficiency of C}\\ & =4-3\\ & =1\\ & \text{Efficiency of A}\\ & =4-2\\ & =2\\ & \text{Efficiency of B}\\ & =4-1\\ & =3\\ & \text{Efficiency of A}+\text{C}\\ & =2+1\\ & =1\\ & \text{Time taken by A}+\text{C}\\ & =\frac{24}{3}\\ & =8\text{ days}\end{array}$$