A small town has only 500 residents. Must there be 2 residents who have the same birthday? Why?
Whether there must be 2 residents having the same birthday, if there are 500 residents.
There are 500 residents.
The generalized pigeonhole principle states that if objects are placed into boxes, then there is at least one box containing at least objects.
Suppose each day of the year is a pigeon hole.
So, there are 365 pigeon holes