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Leaving Cert '11/'12 Off-Topic 2

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    #1712
    LoonyLovegood
    Moderators, Music Moderators, Social & Fun Moderators Posts: 6,068 Mod ✭✭✭✭LoonyLovegood


    Probability of two poets coming up is 25%, I think...That section of maths confuses me.


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    #1713
    Canard
    Moderators, Education Moderators Posts: 8,572 Mod ✭✭✭✭Canard


    Yeah, it seems simple but my brain imploded thinking about it. It might be a bernoulli trial but i really dont know :L


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    #1714
    Wesc.
    Registered Users Posts: 715 ✭✭✭Wesc.


    Togepi wrote: »
    Can any mathsy person work out the probability of having at least 2 of your poets come up on the day if you study 5?

    I tried it and I got 93%, surely that's way off?!

    I got 35.7 % chance for getting 2... I could be wrong because probability is my most hated section!


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    #1715
    Togepi
    Closed Accounts Posts: 4,813 ✭✭✭Togepi


    CTYIgirl wrote: »
    Probability of two poets coming up is 25%, I think...That section of maths confuses me.

    Yeah but I'm looking for the possibility of two or more coming up so it's trickier.



    I tried getting the probability of 0 of them coming up and adding it to the probability of just 1 of them coming up, then I took that away from 1. I'm gonna try again though I think I can see one part where I went wrong. :cool:


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    #1716
    Togepi
    Closed Accounts Posts: 4,813 ✭✭✭Togepi


    I'm so confused. :pac:


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    #1717
    David1994
    Registered Users Posts: 1,073 ✭✭✭David1994


    Just back from work and I am completely wrecked.
    Chemistry questions and a Spanish essay to be done.. Lets get this party started!!


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    #1718
    Togepi
    Closed Accounts Posts: 4,813 ✭✭✭Togepi


    Okay I tried it again...

    Probability of just 1 of my 5 poets coming up is:

    1/8 x 7/8 x 7/8 x 7/8 x 7/8 = 0.07327

    Then I need to multiply that by 5 to take all 5 poets into account (I left this step out the first time):

    0.07327 x 5 = 0.36636

    (Add 0 which is the probability of none coming up.)

    Then take the answer away from 1:

    1 - 0.36636 = 0.63364

    = 63.4%

    = 63%

    That has to be right!! :P


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    #1719
    Wesc.
    Registered Users Posts: 715 ✭✭✭Wesc.


    Togepi wrote: »
    I'm so confused. :pac:

    I did it like this:
    You want the probability of two coming up. So that's, one and another again. The probability of getting one is 5/8 and another one is 4/7.
    Since it's one and another you multiply them and that's how I got 35.7%.


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    #1720
    Eathrin
    Registered Users Posts: 8,076 ✭✭✭Eathrin


    Don't fearses I haz de anser guyz.
    31.5%
    It's unlikely that only 2 would come up.
    Even more unlikely when you take away the maths and consider the trends.


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    #1721
    Togepi
    Closed Accounts Posts: 4,813 ✭✭✭Togepi


    Wesc. wrote: »
    I did it like this:
    You want the probability of two coming up. So that's, one and another again. The probability of getting one is 5/8 and another one is 4/7.
    Since it's one and another you multiply them and that's how I got 35.7%.

    Ah I was wondering how you got 35.7%, I forgot that the second one would be 4/7 not 5/8 again. I was looking for the probability of at least two though, so I had to do it the way I posted above. It seems to have worked out ok... :o


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    #1722
    galwaymusic
    Closed Accounts Posts: 151 ✭✭galwaymusic


    The change of mind is free right?? I've changed it around a bit twice since it opened a few days ago...it only crossed my mind now that I might be charged lol!


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    #1723
    Togepi
    Closed Accounts Posts: 4,813 ✭✭✭Togepi


    Eathrin wrote: »
    Don't fearses I haz de anser guyz.
    13.5%
    It's unlikely that only 2 would come up.
    Even more unlikely when you take away the maths and consider the trends.

    How did you get that?! :(

    And I'm taking 2 coming up as a fantastic scenario, I have 5 done and 4 of them are the 4 most unlikely ones to come up, so I'd be delighted with 2! :D


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    #1724
    deathbythelc
    Registered Users Posts: 338 ✭✭deathbythelc


    And people say you never use Maths outside of school. :D :rolleyes:


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    #1725
    Eathrin
    Registered Users Posts: 8,076 ✭✭✭Eathrin


    Togepi wrote: »
    How did you get that?! :(

    And I'm taking 2 coming up as a fantastic scenario, I have 5 done and 4 of them are the 4 most unlikely ones to come up, so I'd be delighted with 2! :D

    Sorry I corrected myself it's 31.5% I think.


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    #1726
    Togepi
    Closed Accounts Posts: 4,813 ✭✭✭Togepi


    Eathrin wrote: »
    Sorry I corrected myself it's 31.5% I think.

    Okay how did you get 31.5% then? :P Is my 63% completely off?


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    #1727
    Wesc.
    Registered Users Posts: 715 ✭✭✭Wesc.


    Well if it's at least what I'd do is add up the probability of getting 2,3 or 4.
    So that's .357 + .1786 + .071 which is .607 or 60.7%

    That doesn't seem right either :o


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    #1728
    Coeurdepirate
    Registered Users Posts: 2,576 ✭✭✭Coeurdepirate


    Haven't done a tap since Saturday afternoon.


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    #1729
    Togepi
    Closed Accounts Posts: 4,813 ✭✭✭Togepi


    Wesc. wrote: »
    Well if it's at least what I'd do is add up the probability of getting 2,3 or 4.
    So that's .357 + .1786 + .071 which is .607 or 60.7%

    That doesn't seem right either :o

    Yeah that's exactly what I was going to do, I just thought the '1 - the probability of 0 or 1 coming up' was easier.


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    #1730
    Eathrin
    Registered Users Posts: 8,076 ✭✭✭Eathrin


    I misread, my probability was for exactly two.
    There's a 92% chance of at least two appearing.
    Edit: 98% chance, typo.


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    #1731
    Meowth
    Closed Accounts Posts: 1,918 ✭✭✭Meowth


    Sitting in study kill me now :( why did I opt for this :(


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    #1732
    Eathrin
    Registered Users Posts: 8,076 ✭✭✭Eathrin


    Last time I'll correct myself, It's a 98% chance at least 2 will come up if you study 5.


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    #1733
    Togepi
    Closed Accounts Posts: 4,813 ✭✭✭Togepi


    Kinda hope that comes up as a Paper II question in June now. :pac:


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    #1734
    Coeurdepirate
    Registered Users Posts: 2,576 ✭✭✭Coeurdepirate


    Historykitten wrote: »
    Sitting in study kill me now :( why did I opt for this :(

    What time is your study from on what days? Mine is from 6-10 on weekdays and 10-4 on Saturdays. so depressing


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    #1735
    finality
    Registered Users Posts: 1,763 ✭✭✭finality


    If you study 5 the probability of 1 coming up is 1- it's definite. The probability of another one coming up is 4/7. So you've got 1x4/7. That means there's a 57% chance you'll have a choice on the paper.


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    #1736
    Togepi
    Closed Accounts Posts: 4,813 ✭✭✭Togepi


    finality wrote: »
    If you study 5 the probability of 1 coming up is 1- it's definite. The probability of another one coming up is 4/7. So you've got 1x4/7. That means there's a 57% chance you'll have a choice on the paper.

    Any idea what the probability of having either 2 or 3 or 4 of your 5 poets coming up is?


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    #1737
    finality
    Registered Users Posts: 1,763 ✭✭✭finality


    Togepi wrote: »
    Any idea what the probability of having either 2 or 3 or 4 of your 5 poets coming up is?

    I think Eathrin is right with 98%, that's what I'm getting too.

    edit: Aagh but it's so confusing


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    #1738
    PictureFrame
    Registered Users Posts: 3,989 ✭✭✭PictureFrame


    finality wrote: »
    I think Eathrin is right with 98%, that's what I'm getting too.

    edit: Aagh but it's so confusing
    How are you so good at Maths finality? Were you always good in like Primary School or whatever? I'd love an auld Mathsy brain. <3


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    #1739
    Eathrin
    Registered Users Posts: 8,076 ✭✭✭Eathrin


    Okay I am 100% sure I have the answer now. No question.
    The probability of at least 2 poets coming up having studied 5 is exactly 92.86%.


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    #1740
    Wesc.
    Registered Users Posts: 715 ✭✭✭Wesc.


    Eathrin wrote: »
    Okay I am 100% sure I have the answer now. No question.
    The probability of at least 2 poets coming up having studied 5 is exactly 92.86%.

    How'd you go about doing it?


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    #1741
    Eathrin
    Registered Users Posts: 8,076 ✭✭✭Eathrin


    Wesc. wrote: »
    How'd you go about doing it?

    No method springs to mind. In Bernoulli trials I think the events have to be independent, that's where I first went wrong. I'm certain there's a way to do it regularly but I'm yet go figure that out.

    8C4 gives 70 possible outcomes.
    There are only 5 possible outcomes where only one studied poet comes up. I.e post 6 7 and 8 with each of the first 5 poets.
    So 1-5/70 is 93%


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