SSC CHSL 15 Nov 2015 Shift 2 Paper

Let total work = L.C.M. (24,5,12) = 120 units
A can complete the work in 24 days, ⇒ A's efficiency = $\frac{120}{24}=5$ units/day
Similarly, B's efficiency = $\frac{120}{5}=24$ units/day
and C's efficiency = $\frac{120}{12}=10$ units/day
Thus, working together, 1 day work of (A+B+C) = $5+24+10=39$ units
∴ Working together, they will complete the same work in = $\frac{120}{39}$
= $\frac{40}{13}=3\frac{1}{13}$ days