A gambler has in his pocket two fair coins and one two-headed coin. He selects one of the coins at random; when he flips it, it shows heads. What is the probability that it is the two-headed coin? Supposed that he flips the same coin a second time and again it shows heads. What is now the probability that it is the two-headed coin? Supposed that he flips the same coin a third time and it shows heads. What is now the probability that is the two-headed coin?