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 individual odds of each flip is always 50/50. It always is that way those are just your two options.

Now the odds do change when you talk about stringing MULTIPLE flips together.

For example let’s say you flip the coin twice, the odds of getting two heads are 1/4 or 25%. For each individual flip it is still 50/50, but to get that specific whole string of flips it is 25% because you could get:

Heads-heads
Heads-tails
Tails-heads
Tails-tails

There are 4 possible outcomes for a two flip string, meaning each outcome has a 25% chance of happening.

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