Answer
The pigeonhole principle states that if n pigeons (items) are put into m holes (containers), with n > m, then at least one container must contain more than one item.
Work Step by Step
Here, we have 3 socks (pigeons) and two colors(holes, containers, classifiers).
Also, 3>2.
Therefore by pigeonhole principle, we have at least one color which contains more than one($\geq2$) sock which is just a fancy way to say that at least one color is assigned two socks or simply that we have a pair either in black or in blue.
