`1`. Rút gọn phân số
$\dfrac{48}{196}$ `=` $\dfrac{48 : 4}{196 : 4}$ `=` $\dfrac{12}{49}$
$\dfrac{60}{150}$ `=` $\dfrac{60 : 30}{150 : 30 }$ `=` $\dfrac{2}{5}$
$\dfrac{54}{128}$ `=` $\dfrac{54 : 2}{128 : 2}$ `=` $\dfrac{27}{64}$
`2` . Quy dồng mẫu số
`a``)` $\dfrac{2}{3}$ và $\dfrac{4}{7}$
$\text{MSC : 21}$
$\dfrac{2}{3}$ `=` $\dfrac{2 × 7}{3 × 7 }$ `=` $\dfrac{14}{21}$
$\dfrac{ 4×3}{7×3}$ `=` $\dfrac{12}{21}$
`b``)` $\dfrac{5}{4}$ và $\dfrac{9}{20}$
$\text{Giữ nguyên }$$\dfrac{9}{20}$
$\text{MSC : 20}$
$\dfrac{20}{4}$ `=` `5`
$\dfrac{20}{20}$ `=` `1`
$\dfrac{5}{4}$ `×` $\dfrac{5}{5}$ `=` $\dfrac{25}{20}$
`c``)` $\dfrac{3}{4}$ và $\dfrac{4}{5}$
$\text{MSC : 20}$
$\dfrac{3}{4}$ `=` $\dfrac{3 × 4}{4 × 5 }$ `=` $\dfrac{15}{20}$
$\dfrac{4}{5}$ `=` $\dfrac{4× 4 }{5× 4 }$ `=` $\dfrac{16}{20}$
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