$\frac{3}{4}$ và $\frac{4}{5}$     

• $\frac{3}{4}= \frac{3\times 5}{4\times 5}= \frac{15}{20}$
• $\frac{4}{5}= \frac{4\times 4}{5\times 4}= \frac{16}{20}$

=> $\frac{15}{20}$ < $\frac{16}{20}$ (vì 15 < 16)

$\frac{2}{5}$ và $\frac{3}{10}$  

• $\frac{2}{5}= \frac{2\times 2}{5\times 2}= \frac{4}{10}$
• $\frac{3}{10}= \frac{3\times 1}{10\times 1}= \frac{3}{10}$ 

=> $\frac{4}{10}$ > $\frac{3}{10}$ (vì 4> 3)

$\frac{5}{6}$ và $\frac{7}{8}$

• $\frac{5}{6}= \frac{5\times 4}{6\times 4}= \frac{20}{24}$
• $\frac{7}{8}= \frac{7\times 3}{8\times 3}= \frac{21}{24}$

=> $\frac{20}{24}$ < $\frac{21}{24}$ (vì 20 < 21)