Is this amazing or standard? - Gambling and Probability

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Is this amazing or standard?

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01-21-2012 , 11:10 AM

jokerthief

No reason to get excited

Join Date: May 2004 Posts: 4,765

I created a little game where I flip two coins. I did 27 flips and only got one tails, tails. What is the probability of that happening? I'm kinda spooked out.

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01-21-2012 , 11:11 AM

donniccolo

Carpal \'Tunnel

Join Date: Nov 2008 Posts: 6,141

Rigged

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01-21-2012 , 11:36 AM

RustyBrooks

Carpal \'Tunnel

Join Date: Feb 2006 Posts: 24,647

On any particular iteration of this game there is a 1/4 chance of getting TT. So you can run this through a binomial calculator or use BINOMDIST in excel. I used this one:
http://stattrek.com/tables/binomial.aspx
with
prob=.25
trials=27
successes=<=1
and I got .42% or 1/238

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01-21-2012 , 11:46 AM

jokerthief

No reason to get excited

Join Date: May 2004 Posts: 4,765

Thanks Rusty. That's a lot less rare than I thought it would be but still pretty amazing.

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01-23-2012 , 11:05 AM

Ratamahatta

Pooh-Bah

Join Date: Aug 2005 Posts: 4,157

What Rusty said. But the real question should be: what is the probability of me being spooked out after flipping two coins 27 times in a row. This is the same as probability of getting a "weird" outcome (weird outcome = outcome which would spook you out). Getting only one {tail, tail} is only one of them. Adding a sequence with only one {head, head} (which I assume would also spook you out) would double that probability. If you keep adding "weird" sequences and calculate combined probability, you will realize that the probability of getting a weird outcome is not that tiny as you might think and these outcomes are not that spooky

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01-23-2012 , 04:52 PM

theskillzdatklls

Pooh-Bah

Join Date: May 2008 Posts: 4,919

either you're spooked out or you're not.
that's life.

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