posted by Jean .
In a survey of students about favorite sports the results include 23 who like tennis 24 like football 7 like tennis and football 20 like football and baseball 5 like all three sports 9 like no sports. How many students like only tennis and football? How many like only tennis and baseball? How many like only baseball and football?
If you build a Venn diagram for this, you can just read off the numbers.
Start with the 5 who like all three sports, and subtract that from the regions which like two or one.
The 9 who like nothing don't count.