Published online by Cambridge University Press: 01 August 2016
Consider the statement (whose truth is obvious):
If n objects are placed in k boxes, where n = qk + r, q and r are positive integers, and 0 < r < k, then at least one box contains more than q objects.
This is known as a pigeon-hole principle (or Dirichlet’s). It is one of the strategies which is often used for problem-solving. Although it is one of the most powerful tools of combinatorics, the principle can be used successfully in other branches of mathematics. Below you can find a collection of problems which can be solved easily by applying this principle to geometrical objects.