Show that $P(0<Xdfrac23$

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Show that $P(0<X<6)>dfrac23$, if $X$ has probability density function $f(x)=dfrace^-xx^22$, if $x>0$ and $0$, otherwise.




Now, $E(X)=3$ and $Var(X)=3$, so I can not use Chebyshev's inequality. Moreover I used the inequality, $e^-xgeq dfracx^22-x+1$, but also this not working here.



What inequality I should use here? Thanks for any help.







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    up vote
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    down vote

    favorite













    Show that $P(0<X<6)>dfrac23$, if $X$ has probability density function $f(x)=dfrace^-xx^22$, if $x>0$ and $0$, otherwise.




    Now, $E(X)=3$ and $Var(X)=3$, so I can not use Chebyshev's inequality. Moreover I used the inequality, $e^-xgeq dfracx^22-x+1$, but also this not working here.



    What inequality I should use here? Thanks for any help.







    share|cite|improve this question






















      up vote
      1
      down vote

      favorite









      up vote
      1
      down vote

      favorite












      Show that $P(0<X<6)>dfrac23$, if $X$ has probability density function $f(x)=dfrace^-xx^22$, if $x>0$ and $0$, otherwise.




      Now, $E(X)=3$ and $Var(X)=3$, so I can not use Chebyshev's inequality. Moreover I used the inequality, $e^-xgeq dfracx^22-x+1$, but also this not working here.



      What inequality I should use here? Thanks for any help.







      share|cite|improve this question













      Show that $P(0<X<6)>dfrac23$, if $X$ has probability density function $f(x)=dfrace^-xx^22$, if $x>0$ and $0$, otherwise.




      Now, $E(X)=3$ and $Var(X)=3$, so I can not use Chebyshev's inequality. Moreover I used the inequality, $e^-xgeq dfracx^22-x+1$, but also this not working here.



      What inequality I should use here? Thanks for any help.









      share|cite|improve this question











      share|cite|improve this question




      share|cite|improve this question










      asked Aug 27 at 12:42









      Stat_prob_001

      276111




      276111




















          2 Answers
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          $mathbbP(0<X<6) = 1 - mathbbP(|X-mathbbE(X)|geq 3)$.



          Now you can try with Chebyshev's inequality.






          share|cite|improve this answer



























            up vote
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            We have that
            $$P(0<X<6)=int_0^6f(x)mathrmdx$$
            $$=frac12int_0^6e^-xx^2mathrmdx$$
            $$=frac12left.e^-x(-x^2-2x-2)right|_x=0^6$$
            $$=1-25e^-6 approx 0.93803>frac23$$






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              2 Answers
              2






              active

              oldest

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              2 Answers
              2






              active

              oldest

              votes









              active

              oldest

              votes






              active

              oldest

              votes








              up vote
              4
              down vote



              accepted










              $mathbbP(0<X<6) = 1 - mathbbP(|X-mathbbE(X)|geq 3)$.



              Now you can try with Chebyshev's inequality.






              share|cite|improve this answer
























                up vote
                4
                down vote



                accepted










                $mathbbP(0<X<6) = 1 - mathbbP(|X-mathbbE(X)|geq 3)$.



                Now you can try with Chebyshev's inequality.






                share|cite|improve this answer






















                  up vote
                  4
                  down vote



                  accepted







                  up vote
                  4
                  down vote



                  accepted






                  $mathbbP(0<X<6) = 1 - mathbbP(|X-mathbbE(X)|geq 3)$.



                  Now you can try with Chebyshev's inequality.






                  share|cite|improve this answer












                  $mathbbP(0<X<6) = 1 - mathbbP(|X-mathbbE(X)|geq 3)$.



                  Now you can try with Chebyshev's inequality.







                  share|cite|improve this answer












                  share|cite|improve this answer



                  share|cite|improve this answer










                  answered Aug 27 at 12:49









                  LucaMac

                  1,20114




                  1,20114




















                      up vote
                      4
                      down vote













                      We have that
                      $$P(0<X<6)=int_0^6f(x)mathrmdx$$
                      $$=frac12int_0^6e^-xx^2mathrmdx$$
                      $$=frac12left.e^-x(-x^2-2x-2)right|_x=0^6$$
                      $$=1-25e^-6 approx 0.93803>frac23$$






                      share|cite|improve this answer
























                        up vote
                        4
                        down vote













                        We have that
                        $$P(0<X<6)=int_0^6f(x)mathrmdx$$
                        $$=frac12int_0^6e^-xx^2mathrmdx$$
                        $$=frac12left.e^-x(-x^2-2x-2)right|_x=0^6$$
                        $$=1-25e^-6 approx 0.93803>frac23$$






                        share|cite|improve this answer






















                          up vote
                          4
                          down vote










                          up vote
                          4
                          down vote









                          We have that
                          $$P(0<X<6)=int_0^6f(x)mathrmdx$$
                          $$=frac12int_0^6e^-xx^2mathrmdx$$
                          $$=frac12left.e^-x(-x^2-2x-2)right|_x=0^6$$
                          $$=1-25e^-6 approx 0.93803>frac23$$






                          share|cite|improve this answer












                          We have that
                          $$P(0<X<6)=int_0^6f(x)mathrmdx$$
                          $$=frac12int_0^6e^-xx^2mathrmdx$$
                          $$=frac12left.e^-x(-x^2-2x-2)right|_x=0^6$$
                          $$=1-25e^-6 approx 0.93803>frac23$$







                          share|cite|improve this answer












                          share|cite|improve this answer



                          share|cite|improve this answer










                          answered Aug 27 at 12:48









                          Botond

                          4,0082632




                          4,0082632



























                               

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