Introduction:
Today I start learning Pigeonhole Principle. That is another very easy kind of math problems. Wait… I said very easy, but if we look at the past I didn't understood anything about Pigeonhole Principle. After this note, please comment did it look easy or difficult.

The exercise:

In a drawer there are 10 red socks, 10 blue socks, and 10 green socks.
Without looking, how many socks do you need to take out to be 100% sure that you have at least two socks of the same color?

We will work on this exercises. 
And yeah I know - some of you guys will know how to solve this. Others no. Let's say from where I am. I am in the middle. Or that was before I understood it. So let's start.

The solution:
The solution always start when we look the worst situation. Here they need to take two socks with the same color, so the worst situation will be to take one sock from each color.

First extraction: We take one red sock.
Second extraction: We take one blue sock.
Thirth extraction: We take one green

And now comes the moment with the fourth extraction. But before it let's look what we have so far:
We have one red, blue and green sock.
The forth sock can be red, blue or green.
I hope you understand it. I don't care what is the fourth sock. When we take it the condition is met.

Answer:
And I finally find the answer:
 

We need to take 4 socks.

And one important thing. The Pigeonhole Principle is what we made in this exercise. Here is a more close say for that:
We have 3 drawers and 4 socks. That means that there is one drawer with at least two socks.

End:
That is the Pigeonhole Principle. I don't know if you felt it difficult or easy. Please comment down below how you felt like. Bye!