X can do a piece of work in 'p' days and Y can do the same work in 'q' days . Then the number of days in which X and Y can together do that work is

A

$$\frac{p+q}{2}$$

B

$$\frac{1}{p}+\frac{1}{q}$$

C

$$\frac{pq}{p+q}$$

D

$$pq$$