\[\boxed{\text{140\ (140).\ }\text{Еуроки\ -\ ДЗ\ без\ мороки}}\]
Пояснение.
Решение.
\[\frac{2 \cdot 2,5}{2,5 + 3} = \frac{5}{5,5} = \frac{1}{1,1} = \frac{10}{11}.\]
\[\frac{- 1 \cdot 2}{- 1 + 3} = - \frac{2}{2} = - 1.\]
\[\textbf{б)}\ (3a + 6b)\ :\ \frac{2a^{2} - 8b^{2}}{a + b} =\]
\[= \frac{3 \cdot (a + 2b)}{1} \cdot \frac{a + b}{2 \cdot \left( a^{2} - 4b^{2} \right)} =\]
\[при\ a = 26,\ b = - 12:\]
\[\frac{3 \cdot (26 - 12)}{2 \cdot (26 + 2 \cdot 12)} = \frac{3 \cdot 14}{2 \cdot 50} =\]
\[= \frac{42}{100} = \frac{21}{50}.\]