I have some blue and red sock in my drawer. I have a total of 4 socks. I pick 2 socks and chances that I get a pair of red socks is 1/2.

What is the chance of picking a pair of blue socks?

zero

I had 3 red socks and 1 blue sock.

=> chances of pair of red socks = 1/2

chances of pair of mixed socks = 1/2

chances of pair of red socks = NULL