TITLE: Minimum number of flips to guarantee heads
QUESTION [15 upvotes]: This is a weird problem that popped into my head: given a fair coin, how many flips is required to guarantee heads? 
If I get a tails, then another tails, and another etc., the chance of getting a heads increases every time. But there is still a small chance that I will get another tails. 
This seems to imply that there is no finite number of flips to guarantee a heads. Does this mean that infinity is the correct answer (although infinity isn't a number as far as I understand) or is this question even answerable in the first place?

REPLY [3 votes]: If I get a tails, then another tails, and another etc., the chance of getting a heads increases every time.

no. it's still a fair coin after you throw several tails. it's always 50% odds of heads or tails on the next throw. this is just as superstitious as thinking you're at a hot craps table at the casino.