This document explains the Pigeon-Hole Principle and provides an example problem. The Pigeon-Hole Principle states that if the number of items (pigeons) is greater than the number of categories (holes) they are placed into, then at least one category must contain more than one item. The example problem shows 25 students receiving grades of A, B, or C, demonstrating that with more students than grades, at least nine students must have received the same grade. The document is intended to teach this mathematical concept to students through a visual example.