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Unformatted text preview: ( 29 [ ] V X E X ( ) = 2 SD X V X ( ) ( ) = Unit of V(X) is defects 2 , inches 2 or grams 2 etc. Unit of SD(X) is defects, inches or grams; same as for X Other names V(X)=Var(X)= 2 (sigmasquared) 2 is always positive or zero 4 Compute V(X) r.v. X = number of defects x 1 2 f(x) .3 .5 .2 ( 29 X 2 .81= (0.9) 2 .01= (1.9) 2 1.21= (2.9) 2 E(X) = 0 (.3) + 1 (.5) + 2 (.2) = .9 ( 29 [ ] V X E X ( ) = 2 = .81(.3) + .01 (.5) + 1.21 (.2) = 0.49 5 Compute V(X) a Better way r.v. X = number of defects x 1 2 f(x) .3 .5 .2 X 2 1 4 Use this algebraic equivalence: V X E X ( ) ( ) =2 2 =0.9 and 2 = .81 E(X) = 0(.3) + 1(.5) + 4(.2) = 1.3 V(X) = 1.3  (.9) 2 =.49 SAME! 6...
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 Spring '09
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