$3\frac{2}{5}$ > 3,25 vì $3\frac{2}{5}$ = 3,4
$4\frac{1}{20}$ < 4,2 vì $4\frac{1}{20}$ = 4,05
21,09 < $21\frac{1}{10}$ vì $21\frac{1}{10}$ = 21,1
$8\frac{7}{20}$ = 8,35 vì $8\frac{7}{20}$ = 8,35
$3\frac{2}{5}$ > 3,25 vì $3\frac{2}{5}$ = 3,4
$4\frac{1}{20}$ < 4,2 vì $4\frac{1}{20}$ = 4,05
21,09 < $21\frac{1}{10}$ vì $21\frac{1}{10}$ = 21,1
$8\frac{7}{20}$ = 8,35 vì $8\frac{7}{20}$ = 8,35