1. #1
    JohnGalt2341
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    Probability formula question

    Let's say I decide to flip a fair coin 45 times. What is the formula I would use to figure out what the chances are of getting 28 or more Heads? I'm nearly certain that this is a simple formula but for some reason I can't remember it. Any help is appreciated. Thanks!

  2. #2
    Waterstpub87
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    Probability Mass Function. =binom.dist(28,45,0.5,False)

    Its coming up like 3% or so
    Last edited by Waterstpub87; 12-07-17 at 02:20 PM.
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  3. #3
    JohnGalt2341
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    Quote Originally Posted by Waterstpub87 View Post
    Probability Mass Function. =binom.dist(28,45,0.5,False)

    Its coming up like 3% or so
    Thanks a bunch!

  4. #4
    PeterJohnson
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    Waterstpub be my Jim Cramer for a second what crypto stock besides (Bitcoin) should you advise me to buy,buy,buy!?
    Quote Originally Posted by Waterstpub87 View Post
    Probability Mass Function. =binom.dist(28,45,0.5,False)

    Its coming up like 3% or so

  5. #5
    Bostongambler
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    Is the coin black?

  6. #6
    JohnGalt2341
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    Quote Originally Posted by Bostongambler View Post
    Is the coin black?
    No, but what has a Head and a Tail and has no legs and is often brown?

  7. #7
    Waterstpub87
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    Quote Originally Posted by PeterJohnson View Post
    Waterstpub be my Jim Cramer for a second what crypto stock besides (Bitcoin) should you advise me to buy,buy,buy!?
    Not the person you want to ask. I am normally the person who tell everyone not to buy stuff.

    However, long term, buy an S&P 400 etf.

    Not into crypto stuff at all.

  8. #8
    indio
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    Quote Originally Posted by JohnGalt2341 View Post
    Let's say I decide to flip a fair coin 45 times. What is the formula I would use to figure out what the chances are of getting 28 or more Heads? I'm nearly certain that this is a simple formula but for some reason I can't remember it. Any help is appreciated. Thanks!
    The correct answer is 6.76%

    The 3% answer was erroneous, as the chances of getting EXACTLY 28 heads is 3.1%, whereas since you asked what the chances of getting 28 OR MORE heads is, the correct answer is 6.76%

    https://stattools.crab.org/Calculato...alculator.html
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  9. #9
    Waterstpub87
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    Quote Originally Posted by indio View Post
    The correct answer is 6.76%

    The 3% answer was erroneous, as the chances of getting EXACTLY 28 heads is 3.1%, whereas since you asked what the chances of getting 28 OR MORE heads is, the correct answer is 6.76%

    https://stattools.crab.org/Calculato...alculator.html
    You're right. In excel this would be 1 - Binomdist(27,45,.5,True).

  10. #10
    gojetsgomoxies
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    binomial calculator

  11. #11
    arwar
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    it's different if you flip 45 coins at the same time as opposed to flipping one coin 45 times

  12. #12
    Optional
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    Quote Originally Posted by arwar View Post
    it's different if you flip 45 coins at the same time as opposed to flipping one coin 45 times
    Really? Why?

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  13. #13
    Sam Odom
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    Quote Originally Posted by arwar View Post
    it's different if you flip 45 coins at the same time as opposed to flipping one coin 45 times


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  14. #14
    stevek173
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    200 pts to arwar for a video showing him doing this, and explaining it

    for some reason I can see funnyb doing this flipping 45 coins off of a book and that blonde coming in screaming at him

  15. #15
    JohnGalt2341
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    Quote Originally Posted by stevek173 View Post
    200 pts to arwar for a video showing him doing this, and explaining it

    for some reason I can see funnyb doing this flipping 45 coins off of a book and that blonde coming in screaming at him
    I'll throw in 100 points as well... as long as his explanation defends his argument. So far the only thing I can think of is if 1 or more of the coins is an unfair coin. Other than that... I don't see how his statement could possibly make sense.
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  16. #16
    stevek173
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    Yeah I think he was being funny and I found it to be just that

    300 pts not a bad pot

  17. #17
    Harry N. Lloyd
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    Quote Originally Posted by indio View Post
    The correct answer is 6.76%

    The 3% answer was erroneous, as the chances of getting EXACTLY 28 heads is 3.1%, whereas since you asked what the chances of getting 28 OR MORE heads is, the correct answer is 6.76%

    https://stattools.crab.org/Calculato...alculator.html
    Good work, Indio. It's comforting to know someone around here has half a brain on their shoulders.

    As for the OP, just fade Lang. It's simple, fast, and profitable.

  18. #18
    semibluff
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    Well...the probability of losing a coin is higher if you flip 45 coins at the same time rather than flipping the same coin 45 times.

  19. #19
    arwar
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    sorry for the delay guys, also didn't mean to create such a controversy. while this is a complex issue, for the sake of this discussion, it can probably be demonstrated with a simple example. say you flip 45 fair coins all at once and have a sheet covering the results. as you slide the sheet back say 44 of the coins are tails. the probability of the 45th coin being a tail is astronomical. conversly if you are flipping a single fair coin 45 times and the first 44 are tails - then the probability of the 45th toss being tails is still 1/2.

    i have a quick question about a super bowl LII prop --- did Belichel wear a hoodie at any point during the game?

  20. #20
    arwar
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    also - the binominal distribution works for calculating normal results

  21. #21
    Optional
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    The odds of the 45th coin being a tail in that situation is still 50%

    What happened with the other 44 coins has effect on the result of the 45th.

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  22. #22
    Optional
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    In fact if the other 44 coins all came up tails, I'd be looking for some outside influence and probably consider the tail favorite due to that.
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  23. #23
    arwar
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    flipping the single coin it is definitely 1/2 - i also said that they were fair coins - without getting into metaphysics and gambler fallacy, etc. discussion - the probability of all 45 coins being heads or tails is astronomical - and therein lies the difference. of course a coin has no memory of what came before. just out of curiosity (and of course being of no consequence) i wonder what the probability is of a coin landing on its edge. i would presume it is higher for a nickel.

  24. #24
    JohnGalt2341
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    Quote Originally Posted by arwar View Post
    flipping the single coin it is definitely 1/2 - i also said that they were fair coins - without getting into metaphysics and gambler fallacy, etc. discussion - the probability of all 45 coins being heads or tails is astronomical - and therein lies the difference. of course a coin has no memory of what came before. just out of curiosity (and of course being of no consequence) i wonder what the probability is of a coin landing on its edge. i would presume it is higher for a nickel.
    That would be an interesting study because although extremely rare it's still probably more likely than winning the Powerball. There was a great Twilight Zone episode where the coin landed on it's edge.

  25. #25
    HeeeHAWWWW
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    Apparently 1 in 6000 chance of a US nickel landing on its edge, someone did a study :-)

    https://journals.aps.org/pre/abstrac...ysRevE.48.2547

  26. #26
    ans61201
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    Quote Originally Posted by Optional View Post
    The odds of the 45th coin being a tail in that situation is still 50%

    What happened with the other 44 coins has effect on the result of the 45th.
    It's been a few years since college but it's actually not. I believe they talk about it in the movie 21 with Kevin spacey, there's a term for it. It blew my mind for a few weeks, but mathematically speaking, it's true.

  27. #27
    turbobets
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    Quote Originally Posted by Waterstpub87 View Post
    You're right. In excel this would be 1 - Binomdist(27,45,.5,True).
    Why is 27 successes used and not 28?

  28. #28
    Optional
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    Quote Originally Posted by ans61201 View Post

    It's been a few years since college but it's actually not. I believe they talk about it in the movie 21 with Kevin spacey, there's a term for it. It blew my mind for a few weeks, but mathematically speaking, it's true.
    If you recall the name of the term, I'd like to have my mind blown too.

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  29. #29
    Lenny Zefflin
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    This whole flipping 45 coins at once and if the the first 44 are heads then what are the chances that the 45th is a head as well. First I was thinking it's 50%. I still do but trying to figure out if and why that could be wrong. If you did this 100 trillion times so all the different results of how many heads came up are grouped and the occurences of each reflect the true probabilities then 22 and 23 heads would tie for most occurring. 0 and 45 heads would be the least. 1 and 44 would be the second least. So if 45 would occur Im guessing twice as often as 44 then when you see a partial result that would yield either a 44 or a 45 then it will most likely be a 44 since it's twice as likely a 44 was flipped. Im not sure if my logic is correct. Just throwing it out there. Hmmmmmm...

  30. #30
    LT Profits
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    Quote Originally Posted by ans61201 View Post

    It's been a few years since college but it's actually not. I believe they talk about it in the movie 21 with Kevin spacey, there's a term for it. It blew my mind for a few weeks, but mathematically speaking, it's true.
    Quote Originally Posted by Optional View Post

    If you recall the name of the term, I'd like to have my mind blown too.
    He is probably referring to the Monte Hall problem.


  31. #31
    JohnGalt2341
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    Quote Originally Posted by LT Profits View Post
    He is probably referring to the Monte Hall problem.

    I'm not sure if he was talking about the Monte Hall problem or not but one thing people seem to forget about the Monte Hall Problem is someone is controlling the situation and they can show you a Goat(or an empty door) no matter what your first choice is. A lot of people call it the Monte Hall paradox which is incorrect. It's actually a perceived paradox which is something else entirely.

    There are some situations where percentages can get tricky. Example: Let's say you tested positive for a disease that only 1 in 100,000 people had. However, the test for that disease is only 99.9% accurate. That means for every 1 person that has the disease 10 people will test positive for it that are actually negative. So... if you test positive for this disease it's 10 times as likely to be a false positive than you actually having the disease. So... even if the test is 99.9% accurate it is still likely wrong if you test positive.

  32. #32
    RudyRuetigger
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    Quote Originally Posted by JohnGalt2341 View Post
    I'm not sure if he was talking about the Monte Hall problem or not but one thing people seem to forget about the Monte Hall Problem is someone is controlling the situation and they can show you a Goat(or an empty door) no matter what your first choice is. A lot of people call it the Monte Hall paradox which is incorrect. It's actually a perceived paradox which is something else entirely.

    There are some situations where percentages can get tricky. Example: Let's say you tested positive for a disease that only 1 in 100,000 people had. However, the test for that disease is only 99.9% accurate. That means for every 1 person that has the disease 10 people will test positive for it that are actually negative. So... if you test positive for this disease it's 10 times as likely to be a false positive than you actually having the disease. So... even if the test is 99.9% accurate it is still likely wrong if you test positive.
    sorry bro

    but the guy asking all the probability questions, is not the guy I want answering all the probability questions

    don't reply. I already told you..i proved who is the best all time at win percentages, you have your own agenda at a game no one has heard of reversi? and still want to try to bump your own knowledge

    I think you are a fukkin a loser
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  33. #33
    JohnGalt2341
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    Quote Originally Posted by RudyRuetigger View Post
    sorry bro

    but the guy asking all the probability questions, is not the guy I want answering all the probability questions

    don't reply. I already told you..i proved who is the best all time at win percentages, you have your own agenda at a game no one has heard of reversi? and still want to try to bump your own knowledge

    I think you are a fukkin a loser
    You have no idea what the word "proved" means. Look it up. You didn't even provide any evidence, let alone prove anything.

    At this point you talk about Reversi more than I do.

    When I first started posting again at SBR I completely forgot who you were. I only knew your name from the movie which I like. At first I thought you were some kind of bully that someone needed to stand up to. But now I realize that you're not a bully at all. You're more like a small yelping dog that never shuts the F up. What's the longest you've ever went without insulting someone? 2 minutes? 3 tops? You're a complete embarrassment to SBR. I'm amazed they still let you post on here.

  34. #34
    RudyRuetigger
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    I think you are a bitch

    let me know if you want to PROVE otherwise
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  35. #35
    RudyRuetigger
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    Johngalt:

    only uses this forum for his own benefit

    trying to act like a fukkin hotshot at fukkin REVERSI

    need I say more

    NO

    you USE this forum

    I POST on this forum
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