\[\boxed{\text{6.25.}}\]
\[\textbf{а)}\ 5\frac{3}{10} = 5,3;\ \]
\[7\frac{4}{10} = 7,4;\ \]
\[13\frac{13}{100} = 13,13;\ \]
\[8\frac{21}{100} = 8,21;\ \]
\[9\frac{8}{100} = 9,08;\ \]
\[100\frac{1}{100} = 100,01;\ \]
\[303\frac{303}{1\ 000} = 303,303;\ \]
\[12\frac{25}{1\ 000} = 12,025.\ \]
\[\textbf{б)}\ 324\frac{7}{1\ 000} = 324,007;\ \]
\[9\frac{19}{10\ 000} = 9,0019;\ \]
\[21\frac{407}{100\ 000} = 21,00407;\ \]
\[320\frac{1}{10\ 000} = 320,0001;\ \]
\[\frac{8}{10} = 0,8;\ \]
\[\frac{9}{100} = 0,09;\ \]
\[\frac{1}{100\ 000} = 0,00001.\ \ \ \]