each person knew exactly 22 others at a strange party
Source: New Zealand NZMOC Camp Selection Problems 2010 Juniors 6
September 18, 2021
combinatorics
Problem Statement
At a strange party, each person knew exactly others.
For any pair of people and who knew one another, there was no other person at the party that they both knew.
For any pair of people and who did not know each other, there were exactly six other people that they both knew.
How many people were at the party?