I have a bag which contains three coins. One of them is red on one side, blue on the other; another of them is red on one side and green on the other; and the third is blue on one side and green on the other.
I would like to lay them out on the table so that one of each color is facing up.
I reach into the bag and randomly select a coin. I flip it onto the table and it lands red side up (you cannot see what color is on the other side).
Not wanting to risk flipping another red side up, I reach into the bag and look for a coin with a green side, and place it green side up on the table (once again you have no idea what color is on the other side).
If I were to take the last coin out of the bag and flip it, what is the probability that it will land with a blue side facing up?
The coin left in the bag could be R/B R/G or G/B, which (I think) means that the chance of a blue is 1:3. When the coin is flipped the chance is 1:2, so I would say the probability is 1:6.
Hope I am right!