Round 1: Problem 3

Alice and Bob are bored and want to play a game. “I have an idea,” Alice chimes in. “How about you flip this coin 2009 times and I’ll flip it 2010 times and whoever gets more Heads wins?”
Bob replies, “No, that’s not fair! You’re probably going to win since you get more flips!”
“Fine!” answers Alice. “How about this? You flip the coin 2009 times and I’ll flip it 2010 times and if I get more Heads, I win. If you get more Heads, you win. And, if there’s a tie, we’ll say that you win too.” Bob shrugs his shoulders and agrees to play.
What’s the probability that Alice wins the game? Prove your answer.

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