\[\boxed{\text{919.\ }\text{еуроки}\text{-}\text{ответы}\text{\ }\text{на}\text{\ }\text{пятёрку}}\]
\[\frac{a}{54} \in \left\lbrack \frac{1}{9};\frac{1}{6} \right\rbrack,\ \ a \in N\]
\[то\ есть\ \ \frac{1}{9} \leq \frac{a}{54} \leq \frac{1}{6},\ \ \]
\[где\ a = \left\{ 6;7;8;9 \right\}\]
\[\frac{6}{54},\frac{7}{54},\frac{8}{54},\ \frac{9}{54}\ \in \left\lbrack \frac{1}{9};\frac{1}{6} \right\rbrack.\]