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Possibility pyramid

  1. Oct 16, 2004 #1
    a charge can be either negative or positive, computers only understand once and zeroes and for every good thing there is a bad thing.

    Imagine you have a coin with one 1-side and one 0-side. If you do not flip there is a 100% chance that you won't get anything. If you flip once there is a 50% chance that you will get a 1 and 50% chance that you will get a 0.

    If you flip twice there is a 25% chance that you will get two 0, 25% chance that you get two 1 and 50% chance that you will get one 0 and one 1.

    This is the beginning of a possibility pyramid, it looks like this:

    ------------------------------------1----------------------------0 flips
    -------------------------------1/2-----1/2-----------------------1 flip
    ---------------------------1/4-----2/4-----1/4-------------------2 flips
    -----------------------1/8-----3/8-----3/8-----1/8---------------3 flips
    ------------------1/16----4/16----6/16----4/16----1/16----------4 flips
    --------------1/32----5/32---10/32----10/32---5/32----1/32------5 flips

    What is awesome with this pyramid is that there is a pattern in in it. Does this possibility pyramid have a name? It's wonderful how it makes hard math so simple.
  2. jcsd
  3. Oct 16, 2004 #2


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    This is Pascal's triangle, only you've multiplied the nth row by 2^(-n). (the top row is n=0, the zeroth row)

    It gives the binomial coefficients, which are also the number of ways of choosing a heads/tails sequence. e.g. the row 1 4 6 4 1 tells us [tex](x+y)^4=1x^4y^0+4x^3y^1+6x^2y^2+4x^1y^3+1y^4[/tex].
  4. Oct 16, 2004 #3
    thanx, might binomial coefficients have something to do with possibility in coin flipping?
  5. Oct 16, 2004 #4


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    Let's look at where the coefficient of [tex]x^3y^1[/tex] in [tex](x+y)^4=(x+y)(x+y)(x+y)(x+y)[/tex] comes from. When you expand out these brackets, you have a choice of picking x or y from each [tex](x+y)[/tex] term. This corresponds to a sequence of x's and y's of length 4, you can think of this as a coin with "x" on one side and "y" on the other. The information encoded in the coefficient of [tex]x^3y^1[/tex] is the number of length 4 sequences with 3 x's and 1 y, namely xxxy, xxyx, xyxx, and yxxx. 4 of them, which is the coefficient of [tex]x^3y^1[/tex] when we expand.

    Same idea for all the other coefficients.
  6. Oct 17, 2004 #5
    Perfekt, thank you!
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