Eli5: How do the odds of flipping a coin work?

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I know, 50/50 heads tails right? But help me understand the next step – each coin flip has a 50/50 shot of heads or tails. What I don’t understand is how the likelihood of the next flip doesn’t change. For example if I flipped a coin 10 times and every time it flipped heads, the next flip would be 50/50 tails. Wouldn’t the likelihood of flipping a coin 11 times and having it be heads every time be really low? 0.5^11 = 0.048%?

Here’s the origin of the question. I was at a roulette table and the guy said “it’s been black the last 8 rolls, the next one has to be red.” At first I thought, the next roll will be ~47% black, ~47 red, ~6% 0 or 00 you fucking imbecile. Then I thought to myself, what are the chances that there are no red rolls in 9 rolls, which is well below 1%.

Am I the imbecile?

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40 Answers

Anonymous 0 Comments

The chance of each single toss doesn’t change

The chance of heads = 1/2

The chance of two heads in a row = 1/4

If you have already tossed it once and it was heads, then instead of 4 possibilities for 2 heads in a row, there is only a 1/2 chance, heads or tails. The Tails/heads and the Tails/Tails options don’t apply anymore, you have already eliminated half of the possibilities.

If you toss it 9 times in a row and they are all heads, the chances the 10th one will be heads is still 1/2

The chances in general of tossing 10 heads in a row are very small, but you are already down that path, so the chances of what’s in front of you is still 1/2

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