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Fundamentals of Probability and Statistics for Engineers

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R<strong>and</strong>om Variables <strong>and</strong> <strong>Probability</strong> Distributions 41F X (x)11218–2 –1 0 1 2 3xFigure 3.1 <strong>Probability</strong> distribution function <strong>of</strong> X, F X x), <strong>for</strong> Example 3.1F X (x)1.00.2–1 0 1xFigure 3.2<strong>Probability</strong> distribution function <strong>of</strong> a continuous r<strong>and</strong>om variable X, F X x)3.2.2 PROBABILITY MASS FUNCTION FOR DISCRETE RANDOMVARIABLESLet X be a discrete r<strong>and</strong>om variable that assumes at most a countably infinitenumber <strong>of</strong> values x 1, x2,... with nonzero probabilities. If we denotePX ˆ x i ) ˆ px i ), i ˆ 1, 2, . . ., then, clearly,90 < p…x i †1; <strong>for</strong> all i; =Xp…x i †ˆ1:…3:4†;iTLFeBOOK

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