- Thread starter
- #1

- Thread starter Avro
- Start date

- Thread starter
- #1

- Admin
- #2

- Apr 22, 2018

- 251

You can also use this formula for any sets $A$, $B$, $C$:

$$|A\cup B\cup C|\ =\ |A|+|B|+|C|-|A\cap B|-|B\cap C|-|C\cap A|+|A\cap B\cap C|.$$

So, in this problem, $A$ might be the set of girls playing fall sports, $B$ the set of those playing winter sports, and $C$ the set of those playing spring sports; then you want to find $|A\cap B\cap C|$. Also, note that while you are not given $|A\cap B|$, $|B\cap C|$ or $|C\cap A|$ separately, you