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Math Help - Expected value of X

  1. #1
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    Arrow Expected value of X

    Hi everyone!

    The problem:

    "Let X be a discretely distributed stochastic variable with the probabilitydistribution given in the following table:

    (attached as picture to the post)

    Calculate the expected value of X.
    Decide the probabilities:

    P(X ≥ 0) and P (X ≥ 0 | X ≤ 1)"

    What I have done to solve it so far:


    To calculate the expected value of X:

    E(x) = (-2 x 0,1) + (-1 x 0,1) + (0 x 0,5) + (1 x 0,2) + (2 x 0,1) = 0,1

    To decide the probability of P(X ≥ 0):

    0,5 + 0,2 + 0,1 = 0,8

    To decide the probability of P(X ≥ 0 | X ≤ 1):

    0,5 + 0,2 = 0,7

    The last calculation appears to be wrong and I am not sure why. The two first fit with the answer key, but not the last one (0,5 + 0,2 = 0,7).

    Could anyone help me? Thank you so much!
    Attached Thumbnails Attached Thumbnails Expected value of X-mhf-picture-1.jpg  
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  2. #2
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    Re: Expected value of X

    Quote Originally Posted by Nora314 View Post
    The problem:
    "Let X be a discretely distributed stochastic variable with the probabilitydistribution given in the following table:
    Calculate the expected value of X.
    Decide the probabilities:
    P(X ≥ 0) and P (X ≥ 0 | X ≤ 1)"
     \mathcal{P} (X \ge 0 | X \le 1)=\frac{\mathcal{P}(0\le X\le 1)}{\mathcal{P}(X\le 1)}
    Thanks from Nora314
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  3. #3
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    Re: Expected value of X

    Thank you so much, now I got it!
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