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Random Variable. 2013. Random Variable. Two types Discrete Continuous. Random Variable. Probability mass function Discrete P(X = x i ) = p(x i ) p(x i ) = 1. Random Variable. Probability density function Continuous f(x) = e –x x > 0 P(X = a) = 0 - f(x) dx = 1
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Random Variable 2013
Random Variable • Two types • Discrete • Continuous
Random Variable • Probability mass function • Discrete • P(X = xi) = p(xi) • p(xi) = 1
Random Variable • Probability density function • Continuous • f(x) = e –x x > 0 • P(X = a) = 0 • - f(x) dx = 1 • P(a < x < b) = ab f(x) dx
Random Variable • Expected value • = E(x) • = xi p (xi) • = x f(x) dx
Random Variable • Variance
Random Variable • Standard deviation • Sums of R.V.
The Triangular Distribution • Continuous Distribution
Selecting a Distribution • Theoretical prior knowledge • Random arrival => exponential IAT • Sum of large manufactures => Normal CLT • Compare histogram with probability mass or probability density