Pigeonhole Principle is one of the interesting counting principle theories in Mathematics. The principle says, if there is k+1 pigeons and k holes then, there will be one hole with more than one pigeons. In general, the principle is: if there are n+k pigeons and k holes then, there will be n/k or more pigeons in one hole.
The following article is taken from my original book in Bengali for my Bengali readers. The book “Aro Egaro Ghotonar Gonit, Goniter Ghotona” was published in 2008 by DibyoProaksh, Dhaka, Bangladesh. I can upload its English translation if there is any demand on that.