What did the person say to you that proved his statement ?

Question

You are hanging around in hostel when a person approaches you.

"Leaving the bald people aside, I can bet a hundred bucks that there are two people living in this hostel who have same number of hairs on their heads," he says to you.

You say that you will take the bet. After talking to the man for a couple of minutes, you realize that you have lost the bet.

What did the person say to you that proved his statement ?

Answer 1

It is based on the methodology of counting hairs and sizing of heads. In average every person has x amount of hairs and adults have 11 of total head sizes. The average amount of hairs per cm^2 is taken into account.
Let's say there are n people living in the hostel. If n>11 then at least 2 people have same head size. With same head size and average number of hairs per cm^2 they will have same amount of hairs. A man gave this info and the also the number of people living in the hostel.