\[\boxed{\mathbf{57.}}\]
\[\textbf{а)}\ 11,\ 3,\ 21,\ 4,\ 17:\]
\[3,\ 4,\ 11,\ 17,\ 21.\]
\[Медиана = 11.\]
\[\textbf{б)}\ 25,\ 17,\ 19,\ 28,\ 18:\]
\[17,\ 18,\ 19,\ 25,\ 28.\]
\[Медиана = 19.\]
\[\textbf{в)}\ 25,\ 50,\ 25,\ 29,\ 27,\ 40,\ 28:\]
\[25,\ 25,\ 27,\ 28,\ 29,\ 40,\ 50.\]
\[Медиана = 28.\]