In a group of 30 people, must at lest 3 have been born in the same month? Why?

To show that at least 3 people must have been born in the same month in a group of 30 people.

Given information:

A group of 30 people.

Calculation:

Using the pigeonhole principle- the pigeonhole principle states that there must be at least one box which will contain two or more objects if k+1 objects are put in k boxes.

In the above problem there are 30 pigeons (people) and 12 pigeonholes since there are 12 months in a year.

m=12,n=30

So mn=3012=2