a) Ta có: $\frac{6}{10}$ = $\frac{3×2}{5×2}$ = $\frac{3}{5}$
Vì 3 < 4 nên $\frac{3}{5}$ < $\frac{4}{5}$
Vậy $\frac{6}{10}$ < $\frac{4}{5}$
b) Ta có: $\frac{6}{12}$ = $\frac{2×3}{4×3}$ = $\frac{2}{4}$
Vì 3 > 2 nên $\frac{3}{4}$ > $\frac{2}{4}$
Vậy $\frac{3}{4}$ > $\frac{6}{12}$