\[\boxed{\mathbf{655\ (655).\ }Еуроки\ - \ ДЗ\ без\ мороки}\]
\[1)\frac{0,25 + 1000}{2} = 500,125\]
\[\frac{2}{\frac{1}{0,25} + \frac{1}{1000}} = 0,5\]
\[2)\ \frac{a + b}{2} = 1,25\]
\[\frac{2}{\frac{1}{a} + \frac{1}{b}} = \frac{2}{\frac{a + b}{\text{ab}}} = \frac{2ab}{a + b} = 250\]
\[\frac{5a - 2a^{2}}{2,5} = 250\]
\[5a - 2a^{2} = 625\]
\[- 2a^{2} + 5a - 625 = 0\]
\[2a^{2} - 5a + 625 = 0\]
\[2 \cdot {0,25}^{2} - 5 \cdot 0,25 + 625 \neq 0\]
\[623,75 \neq 0\]
\[Ответ:нельзя.\]