\[\boxed{\text{5.294.}}\]
\[\textbf{а)}\ \frac{8}{25} + \frac{7}{25} + \frac{9}{25} = \frac{8 + 7 + 9}{25} =\]
\[= \frac{15 + 9}{25} = \frac{24}{25}\ \]
\[\textbf{б)}\ \frac{13}{15} - \left( \frac{8}{15} + \frac{4}{15} \right) = \frac{13}{15} - \frac{12}{15} =\]
\[= \frac{1}{15}\ \]
\[\textbf{в)}\ \left( \frac{17}{100} + \frac{27}{100} \right) - \left( \frac{8}{100} + \frac{3}{100} \right) =\]
\[= \frac{44}{100} - \frac{11}{100} = \frac{33}{100}\ \]