$\frac{3}{4} = \frac{3 * 15}{4 * 15} = \frac{45}{60}$;
$\frac{11}{12} = \frac{11 * 5}{12 * 5} = \frac{55}{60}$;
$\frac{2}{5} = \frac{2 * 12}{5 * 12} = \frac{24}{60}$;
$\frac{5}{6} = \frac{5 * 10}{6 * 10} = \frac{50}{60}$.
$\frac{24}{60} < \frac{45}{60} < \frac{50}{60} < \frac{55}{60}$, значит:
$\frac{2}{5} < \frac{3}{4} < \frac{5}{6} < \frac{11}{12}$.