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

You are not the imbecile.

Those tiny chances that it happened 11 straight times are dependent on specific outcomes over the course of 11 instances.

Each individual flip of a coin is 50/50, and that should be particularly apparent.

Another way to think about it is that if you land heads 10 times straight, then the odds that you’ll land heads 11 times straight are RIGHT NOW 50/50. The hard part of the math has already happened.

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