Groups of order $360$ have a subgroup of order $10$












5












$begingroup$


I want to prove that groups of order $360$ must have a subgroup of order $10$.



By Sylow's theorem, the number of Sylow $5$-subgroups $n_5 equiv 1 pmod 5$ and $n_5mid 360$. There are three solutions: $1, 6, 36$ (let me know if I missed any).



If $n_5=1$, then the only one is normal, making the product with an element of order $2$ we get a subgroup of order $10$.



If $n_5=36$, then pick any Sylow $5$-subgroup, $[G:N_{G}(P)]=36$. It follows that $N_G(P)$ is a subgroup of order $10$.



But how to deal with the case when $n_5=6$?










share|cite|improve this question











$endgroup$

















    5












    $begingroup$


    I want to prove that groups of order $360$ must have a subgroup of order $10$.



    By Sylow's theorem, the number of Sylow $5$-subgroups $n_5 equiv 1 pmod 5$ and $n_5mid 360$. There are three solutions: $1, 6, 36$ (let me know if I missed any).



    If $n_5=1$, then the only one is normal, making the product with an element of order $2$ we get a subgroup of order $10$.



    If $n_5=36$, then pick any Sylow $5$-subgroup, $[G:N_{G}(P)]=36$. It follows that $N_G(P)$ is a subgroup of order $10$.



    But how to deal with the case when $n_5=6$?










    share|cite|improve this question











    $endgroup$















      5












      5








      5





      $begingroup$


      I want to prove that groups of order $360$ must have a subgroup of order $10$.



      By Sylow's theorem, the number of Sylow $5$-subgroups $n_5 equiv 1 pmod 5$ and $n_5mid 360$. There are three solutions: $1, 6, 36$ (let me know if I missed any).



      If $n_5=1$, then the only one is normal, making the product with an element of order $2$ we get a subgroup of order $10$.



      If $n_5=36$, then pick any Sylow $5$-subgroup, $[G:N_{G}(P)]=36$. It follows that $N_G(P)$ is a subgroup of order $10$.



      But how to deal with the case when $n_5=6$?










      share|cite|improve this question











      $endgroup$




      I want to prove that groups of order $360$ must have a subgroup of order $10$.



      By Sylow's theorem, the number of Sylow $5$-subgroups $n_5 equiv 1 pmod 5$ and $n_5mid 360$. There are three solutions: $1, 6, 36$ (let me know if I missed any).



      If $n_5=1$, then the only one is normal, making the product with an element of order $2$ we get a subgroup of order $10$.



      If $n_5=36$, then pick any Sylow $5$-subgroup, $[G:N_{G}(P)]=36$. It follows that $N_G(P)$ is a subgroup of order $10$.



      But how to deal with the case when $n_5=6$?







      abstract-algebra group-theory finite-groups






      share|cite|improve this question















      share|cite|improve this question













      share|cite|improve this question




      share|cite|improve this question








      edited Jan 11 at 12:37









      the_fox

      2,58711533




      2,58711533










      asked Sep 9 '18 at 19:17









      No OneNo One

      2,0241519




      2,0241519






















          1 Answer
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          $begingroup$

          If $n_5=6$ and $P$ is a Sylow 5-subgroup, you have $|N_G(P)|=60$. Set $H=N_G(P)$, and we find a subgroup of order $10$ in $H$. Your arguments work.
          In $H$, $n_5$ is either $1$ or $6$. If $n_5=1$, multiply Sylow $5$-subgroup with a cyclic of order $2$. If $n_5=6$ and $Q$ is Sylow $5$-subgroup, then $|N_H(Q)|=10$. So, $N_H(Q)leq Hleq G$ is a subgroup of order $10$.






          share|cite|improve this answer









          $endgroup$













          • $begingroup$
            You already know that $n_5=1$ in $H$ since it has a normal Sylow subgroup.
            $endgroup$
            – Levent
            Jan 11 at 13:08











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          1 Answer
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          active

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          4












          $begingroup$

          If $n_5=6$ and $P$ is a Sylow 5-subgroup, you have $|N_G(P)|=60$. Set $H=N_G(P)$, and we find a subgroup of order $10$ in $H$. Your arguments work.
          In $H$, $n_5$ is either $1$ or $6$. If $n_5=1$, multiply Sylow $5$-subgroup with a cyclic of order $2$. If $n_5=6$ and $Q$ is Sylow $5$-subgroup, then $|N_H(Q)|=10$. So, $N_H(Q)leq Hleq G$ is a subgroup of order $10$.






          share|cite|improve this answer









          $endgroup$













          • $begingroup$
            You already know that $n_5=1$ in $H$ since it has a normal Sylow subgroup.
            $endgroup$
            – Levent
            Jan 11 at 13:08
















          4












          $begingroup$

          If $n_5=6$ and $P$ is a Sylow 5-subgroup, you have $|N_G(P)|=60$. Set $H=N_G(P)$, and we find a subgroup of order $10$ in $H$. Your arguments work.
          In $H$, $n_5$ is either $1$ or $6$. If $n_5=1$, multiply Sylow $5$-subgroup with a cyclic of order $2$. If $n_5=6$ and $Q$ is Sylow $5$-subgroup, then $|N_H(Q)|=10$. So, $N_H(Q)leq Hleq G$ is a subgroup of order $10$.






          share|cite|improve this answer









          $endgroup$













          • $begingroup$
            You already know that $n_5=1$ in $H$ since it has a normal Sylow subgroup.
            $endgroup$
            – Levent
            Jan 11 at 13:08














          4












          4








          4





          $begingroup$

          If $n_5=6$ and $P$ is a Sylow 5-subgroup, you have $|N_G(P)|=60$. Set $H=N_G(P)$, and we find a subgroup of order $10$ in $H$. Your arguments work.
          In $H$, $n_5$ is either $1$ or $6$. If $n_5=1$, multiply Sylow $5$-subgroup with a cyclic of order $2$. If $n_5=6$ and $Q$ is Sylow $5$-subgroup, then $|N_H(Q)|=10$. So, $N_H(Q)leq Hleq G$ is a subgroup of order $10$.






          share|cite|improve this answer









          $endgroup$



          If $n_5=6$ and $P$ is a Sylow 5-subgroup, you have $|N_G(P)|=60$. Set $H=N_G(P)$, and we find a subgroup of order $10$ in $H$. Your arguments work.
          In $H$, $n_5$ is either $1$ or $6$. If $n_5=1$, multiply Sylow $5$-subgroup with a cyclic of order $2$. If $n_5=6$ and $Q$ is Sylow $5$-subgroup, then $|N_H(Q)|=10$. So, $N_H(Q)leq Hleq G$ is a subgroup of order $10$.







          share|cite|improve this answer












          share|cite|improve this answer



          share|cite|improve this answer










          answered Sep 9 '18 at 19:35









          SMMSMM

          2,21859




          2,21859












          • $begingroup$
            You already know that $n_5=1$ in $H$ since it has a normal Sylow subgroup.
            $endgroup$
            – Levent
            Jan 11 at 13:08


















          • $begingroup$
            You already know that $n_5=1$ in $H$ since it has a normal Sylow subgroup.
            $endgroup$
            – Levent
            Jan 11 at 13:08
















          $begingroup$
          You already know that $n_5=1$ in $H$ since it has a normal Sylow subgroup.
          $endgroup$
          – Levent
          Jan 11 at 13:08




          $begingroup$
          You already know that $n_5=1$ in $H$ since it has a normal Sylow subgroup.
          $endgroup$
          – Levent
          Jan 11 at 13:08


















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