#Quabotron

Bài 1
a,$\dfrac{45}{30}$=$\dfrac{45 : 5}{30 : 5}$ = $\dfrac{9}{6}$
b,$\dfrac{12}{24}$=$\dfrac{12 : 4 }{24 : 4}$ = $\dfrac{3}{6}$ 
c,$\dfrac{49}{56}$=$\dfrac{49 : 7}{56 : 7}$ = $\dfrac{7}{8}$
d,$\dfrac{121}{143}$=$\dfrac{121 : 11}{143 : 11}$ = $\dfrac{11}{13}$
Bài 2
a,$\dfrac{35}{45}$=$\dfrac{35 : 5}{45 : 5}$ = $\dfrac{7}{9}$ 
b,$\dfrac{12}{45}$=$\dfrac{12 : 3}{45 : 3}$ =$\dfrac{4}{15}$ 
c,$\dfrac{11}{44}$=$\dfrac{11 : 11}{44 : 11}$ = $\dfrac{1}{4}$
d,$\dfrac{19}{57}$=$\dfrac{19 : 19}{57 : 19}$=$\dfrac{1}{3}$
Bài 3.
MSC:10
10 : 2 = 5
10 : 5 = 2
Ta có : 
$\dfrac{3}{2}$ = $\dfrac{3 × 5}{2 × 5}$=$\dfrac{15}{10}$
$\dfrac{1}{5}$ = $\dfrac{1 × 2}{5 × 2}$ = $\dfrac{2}{10}$
Ta giữ nguyên $\dfrac{7}{10}$
Bài 4.
MSC:28
Ta có:
$\dfrac{3}{4}$=$\dfrac{3 × 7}{4 × 7}$=$\dfrac{21}{28}$
$\dfrac{5}{7}$=$\dfrac{5 × 4}{7 × 4}$=$\dfrac{20}{28}$
$\dfrac{1}{2}$=$\dfrac{1 × 14}{2 × 14}$=$\dfrac{14}{28}$

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