$28 = 2^2 * 7$;
$42 = 2 * 3 * 7$;
$НОК(28;42) = 2^2 * 3 * 7 = 4 * 21 = 84$;
$\frac{3}{28} = \frac{3 * 3}{3 * 28} = \frac{9}{84}$;
$\frac{17}{42} = \frac{2 * 17}{2 * 42} = \frac{34}{84}$.

$15 = 3 * 5$;
$20 = 2^2 * 5$;
$10 = 2 * 5$;
$НОК(10;15;20) = 2^2 * 3 * 5 = 4 * 15 = 60$;
$\frac{4}{15} = \frac{4 * 4}{4 * 15} = \frac{16}{60}$;
$\frac{7}{20} = \frac{3 * 7}{3 * 20} = \frac{21}{60}$;
$\frac{3}{10} = \frac{6 * 3}{6 * 10} = \frac{18}{60}$.

$ \begin{array}{r|l} 104 & 2\\ 52 & 2\\ 26 & 2\\ 13 & 13\\ 1 & \end{array} $
 
$ \begin{array}{r|l} 520 & 2\\ 260 & 2\\ 130 & 2\\ 65 & 5\\ 13 & 13\\ 1 & \end{array} $
$104 = 2^3 * 13$;
$520 = 2^3 * 5 * 13$;
$НОК(104;520) = 2^3 * 5 * 13 = 8 * 5 * 13 = 40 * 13 = 520$;
$\frac{25}{104} = \frac{5 * 25}{5 * 104} = \frac{125}{502}$;
$\frac{37}{520}$.

$12 = 2^2 * 3$;
$18 = 2 * 3^2$;
$20 = 2^2 * 5$;
$НОК(12;18;20) = 2^2 * 3^2 * 5 = 4 * 9 * 5 = 20 * 9 = 180$;
$\frac{1}{12} = \frac{15 * 1}{15 * 12} = \frac{15}{180}$;
$\frac{1}{18} = \frac{10 * 1}{10 * 18} = \frac{10}{180}$;
$\frac{1}{20} = \frac{9 * 1}{9 * 20} = \frac{9}{180}$.

$ \begin{array}{r|l} 132 & 2\\ 66 & 2\\ 33 & 3\\ 11 & 11\\ 1 & \end{array} $
 
$ \begin{array}{r|l} 154 & 2\\ 77 & 7\\ 11 & 11\\ 1 & \end{array} $
$132 = 2^2 * 3 * 11$;
$154 = 2 * 7 * 11$;
$НОК(132;154) = 2^2 * 3 * 7 * 11 = 4 * 3 * 77 = 12 * 77 = 924$;
$\frac{7}{132} = \frac{7 * 7}{7 * 132} = \frac{49}{924}$;
$\frac{9}{154} = \frac{6 * 9}{6 * 132} = \frac{54}{924}$.

$15 = 3 * 5$;
$35 = 5 * 7$;
$21 = 3 * 7$;
НОК(15;21;35) = 3 * 5 * 7 = 15 * 7 = 105;
$\frac{2}{15} = \frac{7 * 2}{7 * 15} = \frac{14}{105}$;
$\frac{3}{35} = \frac{3 * 3}{3 * 35} = \frac{9}{105}$;
$\frac{5}{21} = \frac{5 * 5}{5 * 21} = \frac{25}{105}$.