6 = 2 * 3;
$8 = 2^3$;
$9 = 3^2$;
11 = 11 * 1;
$НОК(6;8;9;11) = 2^3 * 3^2 * 11 = 8 * 9 * 11 = 72 * 11 = 792$;
$\frac{5}{6} = \frac{132 * 5}{132 * 6} = \frac{660}{792}$;
$\frac{8}{9} = \frac{88 * 8}{88 * 9} = \frac{704}{792}$;
$\frac{10}{11} = \frac{72 * 10}{72 * 11} = \frac{720}{792}$;
$\frac{7}{8} = \frac{99 * 7}{99 * 8} = \frac{693}{792}$;
$\frac{660}{792} < \frac{693}{792} < \frac{704}{792} < \frac{720}{792}$;
$\frac{5}{6} < \frac{7}{8} < \frac{8}{9} < \frac{10}{11}$.
Ответ:
$\frac{5}{6}$ − наименьшая;
$\frac{10}{11}$ − наибольшая.

$8 = 2^3$;
$18 = 2 * 3^2$;
$20 = 2^2 * 5$;
$60 = 2^2 * 3 * 5$;
$72 = 2^3 * 3^2$;
$360 = 2^3 * 3^2 * 5$;
$НОК = 2^3 * 3^2 * 5 = 8 * 9 * 5 = 360$;
$\frac{217}{360}$;
$\frac{7}{8} = \frac{45 * 7}{45 * 8} = \frac{315}{360}$;
$\frac{47}{60} = \frac{6 * 47}{6 * 60} = \frac{282}{360}$;
$\frac{17}{20} = \frac{18 * 17}{18 * 20} = \frac{306}{360}$;
$\frac{11}{18} = \frac{20 * 11}{20 * 18} = \frac{220}{360}$;
$\frac{67}{72} = \frac{5 * 67}{5 * 72} = \frac{335}{360}$;
$\frac{217}{360} < \frac{220}{360} < \frac{282}{360} < \frac{306}{360} < \frac{315}{360} < \frac{335}{360}$;
$\frac{217}{360} < \frac{11}{18} < \frac{47}{60} < \frac{17}{20} < \frac{7}{8} < \frac{67}{72}$.
Ответ:
$\frac{217}{360}$ − наименьшая;
$\frac{67}{72}$ − наибольшая.