A man begins flipping coins according to the following rules: He starts with a single coin that he flips. Every time he flips a heads, he removes the coin from the game and then puts out two more coins to add to his stack of coins to flip, every time he flips a tails he simply removes the coin from the game. For example, if he flips a heads on his first flip, he now has two coins. He flips both, if he gets two tails then he has run out of coins. On the other hand if he flipped two heads he would now have four coins to flip. Once he begins flipping, what is the probability that he ever runs out of coins? For a harder challenge check out Challenge 12b.