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Two probability problems

  1. Dec 4, 2006 #1
    1. The problem statement, all variables and given/known data
    The second problem in thispic

    2. Relevant equations

    Second problem: For bernoulli trials, if Sn= x1+x2+...+xn is the number of successes, then E(Sn)=np, V(Sn)=npq, D(Sn)=square root of V(Sn)

    3. The attempt at a solution

    For the 2nd problem I have:
    A.) I do not know what they mean by common distribution.
    Sj = x1+x2+x3+x4+...+xj
    Expected value of Xj= sum of (Xj) * probability of (Xj)
    Variance = (j-1)*(probability of (Xj)) * (1 - probability of (Xj))
    Standard deviation is the square root of variance
    B.) E(Tn)= n * P(Tn)
    V(Tn) = n * P(Tn) * (1-P (Tn))

    C.) For coin tossing:
    E(nth occurance of head) = n * (1/2)
    V(nth offucence of head) = n * (1/2) * (1/2)

    I really am not sure about my work. I have been trying it all day. Any guidance would be helpful. Thank you.
    Last edited by a moderator: Apr 22, 2017
  2. jcsd
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