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Thread: data managment help!

  1. #1
    Nov 2008

    data managment help!

    hi I was wondering if anyone could help me figure this question out I think it is binomial distibution but I'm honestly not sure

    If 20 coins are dropped on a table. what is the probability ( to three decimal places ) that
    a) exactly 12 coins are heads
    b) At least 12 coins are heads
    if anyone could help me that would be great!
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  2. #2
    Oct 2008
    It is in fact the binomial distribution because the trials are independent of each other and you are counting the number of successes with a given number of trials.

    For (a),
    Let X be the number of heads.
    P(X=12) = (20 C 12)*(0.5^12)*(0.5^8)

    I'll let you do the computation yourself.

    For (b),
    Note from (a), the binomial distribution will always be a comination multiplied by 0.5^20
    P(X>=12) = P(X=12)+P(X=13)+P(X=14)+...+P(X=20)
    For each probability, just sub in the X value (eg. P(X=13) = (20 C X)*(0.5^20)

    Once again, I'll leave the computation up to you.
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