$$Totalstudents=20$$

$$Mathclub=13members$$

$$Dramaclub=11members$$

As 9 students are members of both clubs. So 13-9=4 of them are members of the math club only and 11-9=2 are members of the Drama club only.

$$20-(9+4+2)=20-15=5$$

5 students are not members of either club.