Reena, Aastha and Shloka can independently complete a piece of work in 6 hours, 4 hours and 12 hours respectively. If they work together, how much time will they take to complete that piece of work ?

Answer: Option A

$$\begin{array}{rl}& \text{Reena’s 1 hour’s work}=\frac{1}{6}\\ & \text{Aastha’s 1 hour’s work}=\frac{1}{4}\\ & \text{Shloka’s 1 hour’s work}=\frac{1}{12}\end{array}$$

( Reena + Aastha + Shloka )'s 1 hour's work
$$\begin{array}{rl}& =\frac{1}{4}+\frac{1}{6}\text{ + }\frac{1}{12}\\ & \text{ = }\frac{6}{12}\\ & =\frac{1}{2}\end{array}$$
Hence, Reema, Aastha and Shloka together take 2 hours to complete the work.