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Quick, basic probability question

  • 26-04-2006 8:37pm
    #1
    pbsuxok1znja4r
    Closed Accounts Posts: 1,312 ✭✭✭pbsuxok1znja4r


    Well, end of another academic year approches, so commences another of my crash courses in whatever I was supposed to study during the year.

    Anyway, what does x generally signify in probability? I know what x usually means but that line underneath is kind of throwing me off...in my rustiness :o

    And...for 100 flips of a fair coin, why is P(x) = 2^-100 ?


Comments

  • #2
    Enrique Sour Spike
    Posts: 0 CMod ✭✭✭✭ Enrique Sour Spike


    It's been a while, but I would have thought the 2 was representing the fact that there are 2 possible outcomes...

    Could be wrong.


  • #3
    pbsuxok1znja4r
    Closed Accounts Posts: 1,312 ✭✭✭pbsuxok1znja4r


    sorry, that should read P(x) = 2^(-100) !

    But yeah the two definitely represents {1, 0} as the possible outcomes...it's just that bar under the x that I'm clueless about...Our poxy lecturer never seemed to explained this stuff (at least while I was awake).


  • #4
    Enrique Sour Spike
    Posts: 0 CMod ✭✭✭✭ Enrique Sour Spike


    IIRC it shouldn't be there/doesn't mean much
    http://en.wikipedia.org/wiki/Notation_in_probability
    doesn't seem to be standard anyway


  • #5
    pbsuxok1znja4r
    Closed Accounts Posts: 1,312 ✭✭✭pbsuxok1znja4r


    perhaps this particular notation falls under the statistics section of the course...who's to know...


  • #6
    Pherekydes
    Registered Users, Registered Users 2 Posts: 16,195 ✭✭✭✭Pherekydes


    x represents a vector, i.e. a column in a matrix.

    The probability of a string of n heads in n tosses is (1/2)^n

    = 1/(2^n)

    = 2(-n)


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  • #7
    pbsuxok1znja4r
    Closed Accounts Posts: 1,312 ✭✭✭pbsuxok1znja4r


    Ah! Of course! Thanks man :)


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