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Thread: Simple probability question I can't figure out- help please

  1. #1
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    Simple probability question I can't figure out- help please

    Hi, I have a probability question I would appreciate help with. Question: if you flip a coin, and continue to flip it, how many times until you would on average get two heads in a row (in immediate succession)?


    I understand that if you were to flip the coins in groups of two, one in four of those groups would be two heads (HH, HT, TT, TH). What Iím less sure about is if youíre flipping coins one after the other- at what point, after how many flips, would you on average get two heads (the number including the two heads)?
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  2. #2
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    Re: Simple probability question I can't figure out- help please

    The question isn't clear the way you a phrasing it.

    Do you mean what is the expected value of the number of tosses it takes to get two heads in a row?
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  3. #3
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    Re: Simple probability question I can't figure out- help please

    Yes
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    Re: Simple probability question I can't figure out- help please

    Quote Originally Posted by Alexander2013 View Post
    Yes
    $E = \sum \limits_{k=0}^\infty~\left(1-\dfrac 1 2 \right)^k\cdot \dfrac 1 4 \cdot (k+2) = \dfrac 3 2$
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