How to calculate the probability in the following problem?












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Let us consider $f(x)=202+37x+243x^2+a_3x^3$$pmod{257}$, where $a_3$ is randomly chosen from $Bbb{Z}_{257}$. I want to calculate all such $S={f(1),f(2),dots, f(n)}, n<255$ such that $f(t)leq 255$ for all $t=1,2,dots, n$. If $f(t)>255$ for some $t$, then we regerate $a_3$ and this process will continue untill all $f(t)leq 255$. Then what is the probability $Pr(f(t)=r)=?$, $0leq r<257$.



Is my following approach true?

Let $X$ be a random variable in $Bbb{Z}_{256}$, then
$Pr(X=rpmod{256})=Pr(X=0pmod{257})Pr(X=0pmod{256})+Pr(X=1pmod{257})Pr(X=1pmod{256})+Pr(Xneq 0,256pmod{257})Pr(Xneq 0,256pmod{256})$?



I am not sure the above approach true or not.










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    0












    $begingroup$


    Let us consider $f(x)=202+37x+243x^2+a_3x^3$$pmod{257}$, where $a_3$ is randomly chosen from $Bbb{Z}_{257}$. I want to calculate all such $S={f(1),f(2),dots, f(n)}, n<255$ such that $f(t)leq 255$ for all $t=1,2,dots, n$. If $f(t)>255$ for some $t$, then we regerate $a_3$ and this process will continue untill all $f(t)leq 255$. Then what is the probability $Pr(f(t)=r)=?$, $0leq r<257$.



    Is my following approach true?

    Let $X$ be a random variable in $Bbb{Z}_{256}$, then
    $Pr(X=rpmod{256})=Pr(X=0pmod{257})Pr(X=0pmod{256})+Pr(X=1pmod{257})Pr(X=1pmod{256})+Pr(Xneq 0,256pmod{257})Pr(Xneq 0,256pmod{256})$?



    I am not sure the above approach true or not.










    share|cite|improve this question









    New contributor




    MKS is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
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    $endgroup$















      0












      0








      0





      $begingroup$


      Let us consider $f(x)=202+37x+243x^2+a_3x^3$$pmod{257}$, where $a_3$ is randomly chosen from $Bbb{Z}_{257}$. I want to calculate all such $S={f(1),f(2),dots, f(n)}, n<255$ such that $f(t)leq 255$ for all $t=1,2,dots, n$. If $f(t)>255$ for some $t$, then we regerate $a_3$ and this process will continue untill all $f(t)leq 255$. Then what is the probability $Pr(f(t)=r)=?$, $0leq r<257$.



      Is my following approach true?

      Let $X$ be a random variable in $Bbb{Z}_{256}$, then
      $Pr(X=rpmod{256})=Pr(X=0pmod{257})Pr(X=0pmod{256})+Pr(X=1pmod{257})Pr(X=1pmod{256})+Pr(Xneq 0,256pmod{257})Pr(Xneq 0,256pmod{256})$?



      I am not sure the above approach true or not.










      share|cite|improve this question









      New contributor




      MKS is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
      Check out our Code of Conduct.







      $endgroup$




      Let us consider $f(x)=202+37x+243x^2+a_3x^3$$pmod{257}$, where $a_3$ is randomly chosen from $Bbb{Z}_{257}$. I want to calculate all such $S={f(1),f(2),dots, f(n)}, n<255$ such that $f(t)leq 255$ for all $t=1,2,dots, n$. If $f(t)>255$ for some $t$, then we regerate $a_3$ and this process will continue untill all $f(t)leq 255$. Then what is the probability $Pr(f(t)=r)=?$, $0leq r<257$.



      Is my following approach true?

      Let $X$ be a random variable in $Bbb{Z}_{256}$, then
      $Pr(X=rpmod{256})=Pr(X=0pmod{257})Pr(X=0pmod{256})+Pr(X=1pmod{257})Pr(X=1pmod{256})+Pr(Xneq 0,256pmod{257})Pr(Xneq 0,256pmod{256})$?



      I am not sure the above approach true or not.







      probability polynomials integers






      share|cite|improve this question









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      share|cite|improve this question









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      share|cite|improve this question




      share|cite|improve this question








      edited Jan 8 at 3:35







      MKS













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      asked Jan 8 at 3:29









      MKSMKS

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      Check out our Code of Conduct.






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