Question 52374
If you select a coin and observe that one side is heads, then you still do not know which coin you have. If it is the two headed coin, then the other side is still heads. If it is the heads/tails coin, then the other side is tails. So, the probability of a head on the other side of the coin, given a head on the first side is still 1/2. 

R^2 at SCC