Question

Explain pigeon hole principle. Using this principle show that in any group of 36 people, we can always find 6
people who were born on the same day of week.

Answer 1

this could help... http://en.wikipedia.org/wiki/Pigeonhole_principle

Answer 2

the pigeonhole principle states that if n items are put into m pigeonholes with n > m, then at least one pigeonhole must contain more than one item.
Ie if you have 36 people, and there are 7 days in the week, then there must exist one day when (at least) 6 people are born on the same day, cause you only have those seven options

Answer 3

so if you think about it, even if you line the 36 people up, and give them birthdays in order ie
person 1 = birthday monday
person 2 = birthday tuesday
person 3 = wednesday
etc one of those days of the week will have 6 people, it's impossible for it not to, as there aren't enough days of the week for that many people