$\frac{15}{20}$ и $\frac{18}{24}$, так как:
$\frac{15}{20} = \frac{3 * 5}{4 * 5} = \frac{3}{4}$;
$\frac{18}{24} = \frac{3 * 6}{4 * 6} = \frac{3}{4}$ и
$\frac{3}{4} = \frac{3}{4}$, то:
$\frac{15}{20} = \frac{18}{24}$

$\frac{20}{35}$ и $\frac{16}{28}$, так как:
$\frac{20}{35} = \frac{4 * 5}{7 * 5} = \frac{4}{7}$;
$\frac{16}{28} = \frac{4 * 4}{7 * 4} = \frac{4}{7}$ и
$\frac{4}{7} = \frac{4}{7}$, то:
$\frac{20}{35} = \frac{16}{28}$

$\frac{12}{30}$ и $\frac{15}{25}$, так как:
$\frac{12}{30} = \frac{2 * 6}{5 * 6} = \frac{2}{5}$;
$\frac{15}{25} = \frac{3 * 5}{5 * 5} = \frac{3}{5}$ и
$\frac{2}{5} ≠ \frac{3}{5}$, то:
$\frac{12}{30} ≠ \frac{15}{25}$

$\frac{18}{22}$ и $\frac{27}{33}$, так как:
$\frac{18}{22} = \frac{9 * 2}{11 * 2} = \frac{9}{11}$;
$\frac{27}{33} = \frac{9 * 3}{11 * 3} = \frac{9}{11}$ и
$\frac{9}{11} = \frac{9}{11}$, то:
$\frac{18}{22} = \frac{27}{33}$

$\frac{30}{48}$ и $\frac{36}{56}$, так как:
$\frac{30}{48} = \frac{5 * 6}{8 * 6} = \frac{5}{8} = \frac{5 * 7}{8 * 7} = \frac{35}{56}$ и
$\frac{35}{56} ≠ \frac{36}{56}$, то:
$\frac{30}{48} ≠ \frac{36}{56}$

$\frac{56}{84}$ и $\frac{82}{108}$, так как:
$\frac{56}{84} = \frac{2 * 28}{3 * 28} = \frac{2}{3} = \frac{2 * 36}{3 * 36} = \frac{72}{108}$ и
$\frac{72}{108} ≠ \frac{82}{108}$, то:
$\frac{56}{84} ≠ \frac{82}{108}$

$\frac{121}{77}$ и $\frac{45}{21}$, так как:
$\frac{121}{77} = \frac{11 * 11}{7 * 11} = \frac{11}{7} = \frac{11 * 3}{7 * 3} = \frac{33}{21}$ и
$\frac{33}{21} ≠ \frac{45}{21}$, то:
$\frac{121}{77} ≠ \frac{45}{21}$

$\frac{49}{63}$ и $\frac{34}{85}$, так как:
$\frac{49}{63} = \frac{7 * 7}{9 * 7} = \frac{7}{9} = \frac{7 * 5}{9 * 5} = \frac{35}{45}$;
$\frac{34}{85} = \frac{2 * 17}{5 * 17} = \frac{2}{5} = \frac{2 * 9}{5 * 9} = \frac{18}{45}$ и
$\frac{35}{45} ≠ \frac{18}{45}$, то:
$\frac{49}{63} ≠ \frac{34}{85}$