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Thread: Fun little maths thing

  1. #101
    Chaos silverx2's Avatar
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    Quote Originally Posted by flashpipe1 View Post
    Nice try, but still wrong. It has to do with the original number of cups when the first choice was made...

    back to 1000 cups...silver chooses one, the one he chooses has a 1 in 100 chance of having the ball...loydall takes all the rest away except one and none of the ones he takes away has the ball...now, that one has a 99 in 100 chance of having the ball, the other still only has a 1 in 100 chance...Gerbs comes along and, it seems like it's a 50/50 chance for him...but it's NOT. It's still a 1/99 chance...

    Think about it in probability and reality...

    again thats a different situation.

    the difference is you are removing 1 cup at a time in the first scenario
    and in the second scenario you are removing 998 cups at a time.

    Regardless when you make your final descision you have a 50/50 chance of choosing correct.
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  2. #102
    anyone else hear that? flashpipe1's Avatar
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    lol...nope...

    Only when you start with 2 cups...remember, in the actual problem, the person taking away the other cups KNOWS which ones don't have the coin/ball/person from NYC, etc. THAT is what changes the odds...

    I know what you're saying...there are 2 cups, there's a 50/50 chance...BUT, when you make your original choice and there are MORE than 2 cups, your odds aren't as good...when the person who KNOWS where the object is removes the other cups, it changes the odds for the one remaining cup, but NOT for the cup you already chose...
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  3. #103
    Chaos silverx2's Avatar
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    doenst change the fact that you have a 50% chance of being right.
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  4. #104
    looks like someone needs to take a look at basic statistics

  5. #105
    anyone else hear that? flashpipe1's Avatar
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    Quote Originally Posted by silverx2 View Post
    doenst change the fact that you have a 50% chance of being right.
    haha...wow silver...even you can't hold onto this forever...I feel like my 2 year old when he beats his head against his bedroom door...

    BECAUSE you chose when there were MORE than two cups and there were WORSE odds of you choosing the correct cup, when the other cups are eliminated (by someone who KNOWS the ball isn't under any of them), there are BETTER odds that the other cup has the ball under it...

    After the example with 100 other cups, I just don't see how you can still say there's a 50/50 chance...

    Let's try this...if you had a group of 100 cups and there was $20 under one of them and you had a group of 2 cups and there was $20 under one of them, which group would you want to play "choose the cup" with??

    loydall...are you happy now??
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  6. #106
    Chaos silverx2's Avatar
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    different situation.

    regardless you have a 50% chance of being right.
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  7. #107
    anyone else hear that? flashpipe1's Avatar
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    lol...wait a sec...are you saying you have the same chances of picking the cup with the $20 in a group of 5 cups as you do in a group of 100 cups???

    I know you can't be saying that, right??
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  8. #108
    Chaos silverx2's Avatar
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    you keep changing the amount of cups.
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  9. #109
    anyone else hear that? flashpipe1's Avatar
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    I know...it changes the odds too...doesn't it...

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  10. #110
    Chaos silverx2's Avatar
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    initially yes, in the end no.
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  11. #111
    anyone else hear that? flashpipe1's Avatar
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    I just don't understand how you don't see that selecting a cup from a group of 100 (1 in 100) and then, having someone who knows that the prize isn't under 98 of the other cups (very important part of the equation) and then removing all of those others, still makes the odds on your cup 1 in 100, but the odds on the other cup 99/100.
    It's really straight-forward...

    It's so not 50/50...unless you turned around, they mixed up the two remaining cups and then you turned back around...THEN it would be 50/50...otherwise, it's still 1/99 because you made your choice when the odds were WAY against you and they stacked the odds for the other cup by removing (with inside knowledge) the other empty cups.

    Is there anyone else on this thread who still agrees with silver here???

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  12. #112
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    yes, some what.

    with 3 cups , a ball, and silver had already picked 1 cup:

    current scenario:
    - cup is removed(revealing that no ball inside) the chance of the ball to be in the other cup increase 2/3 since silver already picked one (that only had 1/3 chance) HOWEVER, the chance of silver to pick the right one also increases to 1/2

    conclusion:
    -chance of unselected cup to have a ball is 2/3
    -chance of silver to pick right cup is 1/2
    combine these chances and you will get the true result.

    - lets look at another scenario:
    if another cup is removed(without revealing what's inside) - the chance of the ball to be in one of the cup is still 1/3 AND the chance for silver to pick the right one is still 1/3

    so the things that changes the odd is the fact that silver picked FIRST and the removed cup is REVEALED to be false. Therefore BOTH ODDS have to be considered.

  13. #113
    anyone else hear that? flashpipe1's Avatar
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    Quote Originally Posted by Jujumon View Post
    -chance of unselected cup to have a ball is 2/3
    -chance of silver to pick right cup is 1/2
    combine these chances and you will get the true result.
    Hmm...sort of...because there are two cups, silver has a 50/50 chance of choosing the correct cup...BUT the odds that the correct cup is the one that he didn't choose initially is 2/3. I don't think the odds need to be factored...the fact that there are 2 cups doesn't change the odds that the initial cup only has a 1/3 chance to be correct and the other has a 2/3 chance...

    yes?
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  14. #114
    Chaos silverx2's Avatar
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    regardless i only have a 50% chance of being correct.
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  15. #115
    Hairy Member robbmcaulay's Avatar
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    Yeh. Given a choice you have a 50% chance of finding it. But the odds are it's in the one you didn't choose.
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  16. #116
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    Quote Originally Posted by flashpipe1 View Post
    Hmm...sort of...because there are two cups, silver has a 50/50 chance of choosing the correct cup...BUT the odds that the correct cup is the one that he didn't choose initially is 2/3. I don't think the odds need to be factored...the fact that there are 2 cups doesn't change the odds that the initial cup only has a 1/3 chance to be correct and the other has a 2/3 chance...

    yes?
    Silver has a 1/2 chance of choosing that 2/3 chance of right cup.


    if u dont consider chooser's odd, then that 2/3 odd of right cup would fail.

    for example, same scenario but now there are silver and gerbick playing:

    silver pick cup A, gerbick pick cup B, cup C is removed and nothing inside. so now where is that 2/3 cup? for silver it's cup B, but for gerbick is cup A right? So now they both have equal chance of choosing that 2/3 cup, just dont know which one, therefore that 2/3 cup is irrelevant.

  17. #117
    He has risen! lefteyewilly's Avatar
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    Quote Originally Posted by adit_ya_sharma View Post
    I coded the logic into a flash file just in case anyone want to check out the probability in action:-

    http://megaswf.com/view/169661484b96...2a73375af.html

    It also has a track of number of plays, wins and losses. Till now for me most of the time the ball is appearing in the other cup.
    so i decided to give this a try. I chose cup #2 for all 100 tests and switched my original pick each time. Here are my results:



    I think this pretty much explains the Monty Hall Problem pretty well.

    Nice job aditya!

  18. #118
    say no more loydall's Avatar
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    Quote Originally Posted by silverx2 View Post
    regardless i only have a 50% chance of being correct.

    You're kidding me.

    I've been away all weekend and just checked the board expecting this thread to be dead and buried.

    Earth to silver - it's not 50%

    Dr. Fact is knocking at the door - for Christ's sake why wont you let hime in?

    Please tell me you're joking?

  19. #119
    Chaos silverx2's Avatar
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    Im not kidding you.
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  20. #120
    supervillain gerbick's Avatar
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    wait. why do I have to say "yarr" while taking the cups?

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