Graph Theory question? Assuming that friendship is always mutual, prove that in any group of n  2 persons, there are at least 2 persons with the same number of friends in the group.
How do I answer this question with a graph ?

You can view this as a question about simple graphs, but it will boil down to the pigeon hole principle. Suppose everyone has a different number of friends, so listing those numbers in order yields $\{ 1,...,n-1\}$ or $\{ 0,1,...,n-2\}$ (depending on what kind of assumptions you want to make). Regardless, you have $n-1$ possibilities with $n$ people.
