It's possible a Venn diagram can have three (or more) sets depicted within them. A set of pupils were asked which sports they played in school, from a list of Football, Hockey, Netball and None.

6 people have seen Band Z and Band X, we can now fill this in on our Venn diagram. Finally, if we now look at the Band X circle, we have all the sections complete except for one. Let’s add up ...