Vimal can do a piece of work in 20 days, Vimal and Kamal together can do in 12 days. If Kamal does the work only for half a day daily then in how many days the work will be completed ?

Answer: Option D

Vimal's 1 day work = $$\frac{1}{20}$$
Since, Vimal and Kamal can together complete in 12 days
i.e. (Vimal + Kamal)'s 1 day work = $$\frac{1}{12}$$
Then,
Kamal's 1 day work,
$$=\frac{1}{12}-\frac{1}{20}\Rightarrow \frac{2}{60}\Rightarrow \frac{1}{30}$$
If Kamal Works only for half a day daily, then his 1 day work becomes $$\frac{1}{2}\times \frac{1}{30}$$  = $$\frac{1}{60}$$
Therefore, 1 day work of both Vimal and Kamal,
$$=\frac{1}{20}+\frac{1}{60}\Rightarrow \frac{4}{60}\Rightarrow \frac{1}{15}$$
Hence, the work will be completed in 15 days.