In one of the earliest posts I listed a number of puzzles on socks. Here is another one:
1) Socks in a bag
You put two socks in a bag. For every sock you put in, there is a 50% chance that it is blue and a 50% chance that it is red. I don’t see which colours you put into the bag.
Without looking, I take out one sock and it turns out to be blue. What is the chance that the other is also blue?
If you are puzzled, we have a solution for you.