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Course in Probability Theory

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114 1 LAW OF LARGE NUMBERS . RANDOM SERIESrespectively . In particular, ifconverges to X <strong>in</strong> pr ., then so doesTo prove the last assertion of the corollary, observe that by Theorem 4 .1 .2the relation (2) holds also <strong>in</strong> pr . Hence ifthen we have(3)n(see Exercise 3 of Sec . 4 .1) .The next law of large numbers is due to Kh<strong>in</strong>tch<strong>in</strong>e . Under the strongerhypothesis of total <strong>in</strong>dependence, it will be proved aga<strong>in</strong> by an entirelydifferent method <strong>in</strong> Chapter 6 .Theorem 5 .2 .2 . Let {X„ } be pairwise <strong>in</strong>dependent and identically distributedr .v.'s with f<strong>in</strong>ite mean m . Then we havePROOF .n 1 nJ X i ~- -aJ=1 j=1 n .1=1Sn- -~ m <strong>in</strong> pr .nLet the common d .f. be F so that( -Xi)-+X+O=X <strong>in</strong>pr.00 00M = r(X n ) _JxdF(x), t (jX,,1) =Jlxi dF(x) < oc .00By Theorem 3 .2 .1 the f<strong>in</strong>iteness of (,,'(IX, 1) is equivalent tonMIX, I>n)

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