# One in a Million V. One in a Billion

Probability Level 2

If you had a fair coin, that is one that flips heads and tails evenly, and flipped it 20 times in a row, the odds that all twenty of those flips will be heads is about $1 \text{ in a } 1,000,000$.

If you kept flipping and kept turning up heads, how much​ more flips of heads would you have to get to for the odds to be at least $1 \text{ in a } 1,000,000,000$?

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