[qup]

> half heads, half tails.

> Under the model where the bias is 0.5—a fair coin—the probability of that outcome is (0.5)^20 or about one in a million.

No.

Edit: someone downvoted, ha. It's closer to 1 in 6.

[cj]

1 in a million is the probability of correctly predicting a unique sequence of 20 coin flips, in the exact order. (E.g. first 10 flips heads, 2nd 10 flips tails, in that order - 1 in a million)

[BeetleB]

I'm surprised people are conflating the Binomial distribution with OP's statement. He is talking about one specific outcome of half heads/half tails (where order matters). There is exactly one way to get that outcome.

[qup]

You only knew that because you know how to do the math yourself, friend.

If you read what he said (I quoted it), he was not talking about one specific outcome. He didn't...well, specify that. He said half and half.

I also know how to do math, as I think I proved in my own comment. So I don't accept your insult.

[l_e_o_n]

Edited for clarity.