Mrs. grady surveyed 30 students, 11 of which said they liked basketball, 16 of which said they liked hockey, and 2 of which said they liked both sports.
(a) how many students did not like either sport?
students
(b) how many students liked exactly one of the sports?
students

If 11 like basketball and 16 like hockey, you get a total of 27, but if 2 said both then you don't want to double count them, so a total of 25 students answered. If 25 total students answered but 2 liked both, then 23 only liked one. 

The answer to (a) is 5 students did not like either sport

The answer to (b) is 23 students liked exactly one sport.