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Probability Question - Exponential Distribution

  1. Mar 15, 2013 #1
    1. The problem statement, all variables and given/known data

    Suppose that X has an exponential distribution with mean μ. Find the probability that x lies within one standard deviation of its mean, that is find P(μ-σ≤X≤μ+σ)

    2. Relevant equations

    3. The attempt at a solution

    If I'm not mistaken the standard deviation is equal to the mean of an exponential distribution so isn't the answer just zero or am I missing something important here?
  2. jcsd
  3. Mar 15, 2013 #2

    Ray Vickson

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    Homework Helper

    Yes. You are missing the facts that μ-σ = 0 and μ+σ = 2μ, so you want P(0 ≤ X ≤ 2μ). Why would you suppose that is 0?
  4. Mar 15, 2013 #3
    oh thanks i missed that
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