\[\boxed{\text{878.\ }\text{еуроки}\text{-}\text{ответы}\text{\ }\text{на}\text{\ }\text{пятёрку}}\]
\[\textbf{а)}\ 5 < y < 8\]
\[\frac{1}{8} < \frac{1}{y} < \frac{1}{5}\]
\[\textbf{б)}\ 0,125 < y < 0,25\]
\[\frac{1}{0,125} < \frac{1}{y} < \frac{1}{0,25}\]
\[\frac{1}{\frac{1}{8}} < \frac{1}{y} < \frac{1}{\frac{1}{4}}\]
\[4 < \frac{1}{y} < 8\]