I will have sixteen students in my graph theory course this semester. In our first session I asked each of them with which of the other 15 students in the class they were already acquainted before the course. The graph below is the result, where for convenience students have been labelled 0 through 15.
For a certain activity, I have been able to split the 16 students into three groups. In the first of the groups, everyone was already acquainted with everyone else in the group, while in the second group no one had met any of the other members of the group. The third group was made up of just fourfive students who did not belong to either of the first two groups.