\[\boxed{\text{5.507.}}\]
\[\textbf{а)}\ a < \frac{1}{2} = \frac{6}{12}\]
\[a = \frac{1}{12};\frac{2}{12} = \frac{1}{6};\frac{3}{12} = \frac{1}{4};\frac{4}{12} = \frac{1}{3}.\]
\[\textbf{б)}\ 5 < b < 8\]
\[b = 6;6\frac{1}{2};7;7\frac{3}{4}.\]
\[\textbf{в)}\ 9\frac{1}{2} = 9\frac{6}{12} < c < 10\frac{1}{4} = 10\frac{3}{12}\]
\[c = 9\frac{7}{12};9\frac{11}{12};10;10\frac{1}{12}.\]