Of the 30 students in my class, 11 practice taekwondo, 11 play piano, and 20 take lessons in math. 4 students play piano and go to math, 3 students do taekwondo and play piano, 5 students go to math...

Of the 30 students in my class, 11 practice taekwondo, 11 play piano, and 20 take lessons in math. 4 students play piano and go to math, 3 students do taekwondo and play piano, 5 students go to math and practice taekwondo, and 3 students do none of these. How many students do all 3?