[Toán 7] Helplllllll

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soicon_boy_9x

$\dfrac{b}{a}=2 \rightarrow b=2a$
$\dfrac{c}{d}=3 \rightarrow c=3d$
$\rightarrow \dfrac{a+b}{c+d}=\dfrac{2a+a}{3d+d}=\dfrac{3a}{4d}=\dfrac{3}{4}.\dfrac{a}{d}$
 
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