Problem
COM-B1-M05-P001 Thirteen People
#1
★☆☆☆☆ Level 1 of 5
Prove that among \(13\) people, two were born in the same month.
Months are boxes.
There are \(12\) months and \(13\) people. By the pigeonhole principle, some month contains at least two birthdays.
Basic formulation of the method.