a/ $\dfrac{5}{10}=\dfrac{5:5}{10:5}=\dfrac{1}{2}$
$\dfrac{25}{75}=\dfrac{25:25}{75:25}=\dfrac{1}{3}$
Quy đồng, mẫu số chung $6$
$\dfrac{1}{2}=\dfrac{1×3}{2×3}=\dfrac{3}{6}$
$\dfrac{1}{3}=\dfrac{1×2}{3×2}=\dfrac{2}{6}$
b/ $\dfrac{42}{56}=\dfrac{42:14}{56:14}=\dfrac{3}{4}$
$\dfrac{18}{48}=\dfrac{18:6}{48:6}=\dfrac{3}{8}$
Quy đồng, mẫu số chung $8$
$\dfrac{3}{4}=\dfrac{3×2}{4×2}=\dfrac{6}{8}$
$\dfrac{3}{8}=\dfrac{3}{8}$
c/ $\dfrac{27}{81}=\dfrac{27:27}{81:27}=\dfrac{1}{3}$
$\dfrac{57}{76}=\dfrac{57:19}{76:19}=\dfrac{3}{4}$
$\dfrac{35}{84}=\dfrac{35:7}{84:7}=\dfrac{5}{12}$
Quy đồng, mẫu số chung $12$
$\dfrac{1}{3}=\dfrac{1×4}{3×4}=\dfrac{4}{12}$
$\dfrac{3}{4}=\dfrac{3×3}{4×3}=\dfrac{9}{12}$
$\dfrac{5}{12}=\dfrac{5}{12}$
