I have two coins in my pocket. One of them is normal. One side heads one side tails. The others both sides are tails. So if I pick a random coin from my pocket and the side I see is "tails" what is the probability that the other side is also "tails".
Does the the probability change when I pick one coin?
I'm sorry if this is asked before but I'm not sure about the theory name or how to search for.