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Coin flip

  1. Mar 10, 2006 #1
    If I throw 1000 times a coin what is the probability to have at least one time a difference between heads and tails of 40.
    thank you for yours help
  2. jcsd
  3. Mar 11, 2006 #2


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    If n is the number of heads, m is the number of tails, how would you express your question arithmetically?
  4. Mar 11, 2006 #3


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    The problem you stated is an example of a random walk with one barrier problem. You can find a discussion in any standard probability text. For example Feller (Vol I) is a very good, although old test.
  5. Mar 13, 2006 #4
    I'm sorry but I don't see the solution, It would be easy if I have to stimate the probability after n flip but I have to calculate it dinamically trough the n flips.
    I thougt to make tehe product from 40 to n-40 of (1-Bin(0.5)) but i don't know if is right.
    With 1000 flip --> p=1-0.126 to see a difference of 40 during the test

    Thank you
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