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Math Help - Probability of a (discrete) random variable

  1. #1
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    Probability of a (discrete) random variable

    I'm having trouble understanding this question:

    Suppose the random variable x = 1, 2, 3, 4, 5, 6.
    In addition suppose
    p(1)=p(2) and p(3)=p(4)=p(5)=p(6)
    If the mean μ=4.00, then P(2 ≤ x ≤ 3) is:
    So since all the values of x are laid out, x is a discrete random variable. Since there are only really two distinct probabilities, I'm guessing this would be a binomial distribution.

    The binomial distribution formula is: p(x) = nCx * px * (1-p)n-x

    and since the mean is given, i know the mean = n*p, but I don't know how I'd find either n or p since neither are given

    any ideas?
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  2. #2
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    Re: Probability of a (discrete) random variable

    Quote Originally Posted by snypeshow View Post
    I'm having trouble understanding this question:
    Suppose the random variable x = 1, 2, 3, 4, 5, 6.
    In addition suppose
    p(1)=p(2) and p(3)=p(4)=p(5)=p(6)
    If the mean μ=4.00, then P(2 ≤ x ≤ 3) is:
    This is not binomial.
    You have two probabilities a~\&~b.
    From the given 2a+4b=1 and 3a+18b=4.
    Solve for a~\&~b. The your answer is a+b
    Thanks from snypeshow
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    Re: Probability of a (discrete) random variable

    I understand how you got 2a and 4b, but how did you get 3a and 18b?
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    Re: Probability of a (discrete) random variable

    Quote Originally Posted by snypeshow View Post
    I understand how you got 2a and 4b, but how did you get 3a and 18b?
    How does one find the mean(expected value) of a distribution?
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    Re: Probability of a (discrete) random variable

    Expected value is the sum of x multiplied by its probabilities

    (1+2)a and (3+4+5+6)b

    ok, so I understand that part, but why would you set it to equal 4.0 which is the standard deviation?
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    Re: Probability of a (discrete) random variable

    Quote Originally Posted by snypeshow View Post
    Expected value is the sum of x multiplied by its probabilities

    (1+2)a and (3+4+5+6)b

    ok, so I understand that part, but why would you set it to equal 4.0 which is the standard deviation?
    \text{The standard deviation }\ne\text{ the  mean.}
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    Re: Probability of a (discrete) random variable

    Oh, ok, I gotchya!! Thanks dude!!
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