Các bước giải:.
1,
a,$\dfrac{14}{28}=\dfrac{14}{14×2}=\dfrac{1}{2}$
b,$\dfrac{25}{50}=\dfrac{25}{25×2}=\dfrac{1}{2}$
c,,$\dfrac{48}{30}=\dfrac{48:6}{30:6}=\dfrac{8}{5}$
d,$\dfrac{81}{54}=\dfrac{81:9}{54:9}=\dfrac{9}{6}=\dfrac{3}{2}$
2,
$\dfrac{2}{3}=\dfrac{2×4}{3×4}=\dfrac{8}{12}$
$\dfrac{2}{3}=\dfrac{2×10}{3×10}=\dfrac{20}{30}$
3,
$\dfrac{25}{100}=\dfrac{25:5}{100:5}=\dfrac{5}{20}$
4.
b,$\dfrac{8×7×5}{11×8×7}=\dfrac{5}{11}$
( triệt tiêu được 8×7)
c,$\dfrac{19×2×5}{19×3×5}=\dfrac{2}{3}$
(triệt tiêu được 19×5)
