How many of them chose neither sports nor music ?

Question

100 students entered college.
55 of them chose sports.
44 of them chose music.
20 of them chose both.
How many of them chose neither sports nor music ?

Answer 1

55 + 44 - 20 = 79 of them either chose sports, music or both.
Then 100 - 79 = 21 of them didn't choose either.

Answer 2

1.- 20 chose both sports and music
2.- As the total number of students prefering sports is 55, then 55-20 = 35 students chose music only.
3.- As the total number of students prefering music is 44, then 44 - 20 = 24 students chose sports only
Therefore, 100 - ( 20+35+24) = 21 students chose neither sports nor music