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I need some help with some probability

  1. Feb 29, 2008 #1
    So for general expected value, I know how to do it. Multiply probablity of X to the value of X and add them up. For density function such as

    f(x) = 2x 0<x<1 and 0 otherwise. I take find the integral. I'm just confused when it comes to something like

    f(x) = (x - 8) 8 < x < 9; (10 -x ) 9 < x < 10; 0 otherwise. I hope someone can help me clear this up lolz. Thanks veryyyyyy much
  2. jcsd
  3. Mar 1, 2008 #2
    Here since this is continuous random variable, we can define f(9)=1. Then looking at the graph of x-f(x), we see that the expected value is the sum of the areas under the curve. Hence, for this question the expected value is ((10-8)*1)/2=1, which proves that f is a probability function.
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