A simple probability question about two types of cards There is a hidden box that contains two different types of cards--1 Card A and 1 Card B. Card A has both sides of the card red while Card B has one side red and the other blue. If you randomly picked a card and saw a red face, what is the probability that this card is of type A. Using the conditional probability equation, I seem to be getting $0.5$ as the answer, however, the true answer is $2/3$. And I dont see how you can get $2/3$?

If we assume there are the same number of type 'A' cards as type 'B' cards then if you pull a card at random and look at one side only there are 4 equally likely results
Red or Red from card A.
Red or Blue from card B.
By observing a red face we can eliminate one of these options so we now have only 3 equally likely results and of these how many are using Card A?
Answer 2 of the 3 equally likely outcomes use card A so probability is $\dfrac{2}{3}$.
