11. The Youth Palace is recruiting for spring calligraphy, art, and music instrument classes. The calligraphy class has enrolled 29 students, the art class has enrolled 28 students, and the music instrument class has enrolled 27 students. Among these students, 13 are enrolled in both calligraphy and art, 12 are enrolled in both calligraphy and music instruments, 11 are enrolled in both art and music instruments, and 5 are enrolled in all three subjects. Therefore, the number of students who are only enrolled in one subject is $\qquad$.

【Key Point】Principle of Inclusion and Exclusion
【Difficulty】Adjacent

【Answer】 27
【Solution】Principle of Inclusion and Exclusion. Total number of people: $29+28+27-13-12-11+5=53$ people, $53-13-12-11+5 \times 2=27$ people