You are in your friend's home.You are asked by your friend,

a mathematician to enter a totally dark room and to pick up a pair of socks from a certain drawer.

You are told that there are some socks in that drawer, and that each can be either black or white.

You are told as well that the probability of picking at random two black socks is 1/2.

What is the probability of taking out a pair of white socks from the drawer?

I have generalized the question (originally there were 4 socks) since I was criticized for posting a "too simple " question not meriting even D2.

"Some socks" might apply to 4 or 120 , but not over 4000

Clearly the answer is zero for n=4 and 1/12 for n=120 .

The quantities to consider are limited only by the size of the drawer

and maybe by the amount of time the mathematician spent on preparing this "simple" question.

*Edited on ***September 30, 2015, 12:14 am**