## A card puzzle

Studying for an exam next week, I came across this courtesy of a kind professor in Hong Kong. I think it classifies as a bit of brain teaser, so thought I'd post it here:

Suppose we have 3 cards whose sides are coloured as follows:

- red/red
- black/black
- red/black

A card is chosen at random and placed on the ground. If the upper side of the card is red, what is the probability that the other side is black?

The answer's in the comments...

{2010.01.26 - 16:40}