A, B and C can complete a piece of work in 24, 6 and 12 days respectively. Working together, they will complete the same work in:

Answer: Option C

Formula: If A can do a piece of work in n days, then A's 1 day's work = $$\frac{1}{\text{n}}$$
$$\begin{array}{rl}& (A+B+C{)}^{\prime }s1\text{day’s work}\\ & =\frac{1}{24}+\frac{1}{6}+\frac{1}{12}=\frac{7}{24}\end{array}$$
Formula: If A's 1 day's work = $$\frac{1}{\text{n}}$$ , then A can finish the work in n days
So, all the three together will complete the job in
$$\frac{24}{7}\text{ days}=3\frac{3}{7}\text{ days}$$