Convergence in probability: The inverse of the simple mean












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I have a question on convergence: I have to prove that $frac{n}{U_{n}} longrightarrow 1$ in probability, where $U_{n}=sum X_{i}$, $X_{i}sim mathrm{Exp}(1)$ and because of this, $U_{n}sim mathrm{Gamma}(n,1)$.



This problem had two parts, the other part was to prove that $frac{U_{n}}{n}longrightarrow 1$ in probability which I proved invoking the weak law for big numbers. But this, I have no clue how to prove it.



Thanks so much for your help! :)










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    1












    $begingroup$


    I have a question on convergence: I have to prove that $frac{n}{U_{n}} longrightarrow 1$ in probability, where $U_{n}=sum X_{i}$, $X_{i}sim mathrm{Exp}(1)$ and because of this, $U_{n}sim mathrm{Gamma}(n,1)$.



    This problem had two parts, the other part was to prove that $frac{U_{n}}{n}longrightarrow 1$ in probability which I proved invoking the weak law for big numbers. But this, I have no clue how to prove it.



    Thanks so much for your help! :)










    share|cite|improve this question











    $endgroup$















      1












      1








      1





      $begingroup$


      I have a question on convergence: I have to prove that $frac{n}{U_{n}} longrightarrow 1$ in probability, where $U_{n}=sum X_{i}$, $X_{i}sim mathrm{Exp}(1)$ and because of this, $U_{n}sim mathrm{Gamma}(n,1)$.



      This problem had two parts, the other part was to prove that $frac{U_{n}}{n}longrightarrow 1$ in probability which I proved invoking the weak law for big numbers. But this, I have no clue how to prove it.



      Thanks so much for your help! :)










      share|cite|improve this question











      $endgroup$




      I have a question on convergence: I have to prove that $frac{n}{U_{n}} longrightarrow 1$ in probability, where $U_{n}=sum X_{i}$, $X_{i}sim mathrm{Exp}(1)$ and because of this, $U_{n}sim mathrm{Gamma}(n,1)$.



      This problem had two parts, the other part was to prove that $frac{U_{n}}{n}longrightarrow 1$ in probability which I proved invoking the weak law for big numbers. But this, I have no clue how to prove it.



      Thanks so much for your help! :)







      probability-theory statistics convergence exponential-distribution gamma-distribution






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      edited Nov 29 '18 at 9:56









      Davide Giraudo

      126k16150261




      126k16150261










      asked Nov 28 '18 at 21:25









      DadadaveDadadave

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      9118






















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          $begingroup$

          I think you can use the continuous mapping theorem on the other part of the question.






          share|cite|improve this answer









          $endgroup$













          • $begingroup$
            So I just have to use $g(x)=x^{-1}$, and then, since $frac{U_{n}}{n}$ converges in probability to 1, then $g( frac{U_{n}}{n})= frac{n}{U_{n}}$ converges in probability to $g(1)=1$ ? That simple? Thanks! :)
            $endgroup$
            – Dadadave
            Nov 28 '18 at 22:11






          • 1




            $begingroup$
            Yes. Ideally, you define $g(0)=0$ and note that the set of discontinuity points is indeed a $P_X$-zero-set :) (as $U_n$ can be $0$)
            $endgroup$
            – Stockfish
            Nov 29 '18 at 10:09











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          $begingroup$

          I think you can use the continuous mapping theorem on the other part of the question.






          share|cite|improve this answer









          $endgroup$













          • $begingroup$
            So I just have to use $g(x)=x^{-1}$, and then, since $frac{U_{n}}{n}$ converges in probability to 1, then $g( frac{U_{n}}{n})= frac{n}{U_{n}}$ converges in probability to $g(1)=1$ ? That simple? Thanks! :)
            $endgroup$
            – Dadadave
            Nov 28 '18 at 22:11






          • 1




            $begingroup$
            Yes. Ideally, you define $g(0)=0$ and note that the set of discontinuity points is indeed a $P_X$-zero-set :) (as $U_n$ can be $0$)
            $endgroup$
            – Stockfish
            Nov 29 '18 at 10:09
















          2












          $begingroup$

          I think you can use the continuous mapping theorem on the other part of the question.






          share|cite|improve this answer









          $endgroup$













          • $begingroup$
            So I just have to use $g(x)=x^{-1}$, and then, since $frac{U_{n}}{n}$ converges in probability to 1, then $g( frac{U_{n}}{n})= frac{n}{U_{n}}$ converges in probability to $g(1)=1$ ? That simple? Thanks! :)
            $endgroup$
            – Dadadave
            Nov 28 '18 at 22:11






          • 1




            $begingroup$
            Yes. Ideally, you define $g(0)=0$ and note that the set of discontinuity points is indeed a $P_X$-zero-set :) (as $U_n$ can be $0$)
            $endgroup$
            – Stockfish
            Nov 29 '18 at 10:09














          2












          2








          2





          $begingroup$

          I think you can use the continuous mapping theorem on the other part of the question.






          share|cite|improve this answer









          $endgroup$



          I think you can use the continuous mapping theorem on the other part of the question.







          share|cite|improve this answer












          share|cite|improve this answer



          share|cite|improve this answer










          answered Nov 28 '18 at 21:42









          angryavianangryavian

          40.7k23380




          40.7k23380












          • $begingroup$
            So I just have to use $g(x)=x^{-1}$, and then, since $frac{U_{n}}{n}$ converges in probability to 1, then $g( frac{U_{n}}{n})= frac{n}{U_{n}}$ converges in probability to $g(1)=1$ ? That simple? Thanks! :)
            $endgroup$
            – Dadadave
            Nov 28 '18 at 22:11






          • 1




            $begingroup$
            Yes. Ideally, you define $g(0)=0$ and note that the set of discontinuity points is indeed a $P_X$-zero-set :) (as $U_n$ can be $0$)
            $endgroup$
            – Stockfish
            Nov 29 '18 at 10:09


















          • $begingroup$
            So I just have to use $g(x)=x^{-1}$, and then, since $frac{U_{n}}{n}$ converges in probability to 1, then $g( frac{U_{n}}{n})= frac{n}{U_{n}}$ converges in probability to $g(1)=1$ ? That simple? Thanks! :)
            $endgroup$
            – Dadadave
            Nov 28 '18 at 22:11






          • 1




            $begingroup$
            Yes. Ideally, you define $g(0)=0$ and note that the set of discontinuity points is indeed a $P_X$-zero-set :) (as $U_n$ can be $0$)
            $endgroup$
            – Stockfish
            Nov 29 '18 at 10:09
















          $begingroup$
          So I just have to use $g(x)=x^{-1}$, and then, since $frac{U_{n}}{n}$ converges in probability to 1, then $g( frac{U_{n}}{n})= frac{n}{U_{n}}$ converges in probability to $g(1)=1$ ? That simple? Thanks! :)
          $endgroup$
          – Dadadave
          Nov 28 '18 at 22:11




          $begingroup$
          So I just have to use $g(x)=x^{-1}$, and then, since $frac{U_{n}}{n}$ converges in probability to 1, then $g( frac{U_{n}}{n})= frac{n}{U_{n}}$ converges in probability to $g(1)=1$ ? That simple? Thanks! :)
          $endgroup$
          – Dadadave
          Nov 28 '18 at 22:11




          1




          1




          $begingroup$
          Yes. Ideally, you define $g(0)=0$ and note that the set of discontinuity points is indeed a $P_X$-zero-set :) (as $U_n$ can be $0$)
          $endgroup$
          – Stockfish
          Nov 29 '18 at 10:09




          $begingroup$
          Yes. Ideally, you define $g(0)=0$ and note that the set of discontinuity points is indeed a $P_X$-zero-set :) (as $U_n$ can be $0$)
          $endgroup$
          – Stockfish
          Nov 29 '18 at 10:09


















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