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Ta có : 13/15=1-10/25                 12/25=1-13/25

Vì 10/25 <13/25(so sánh 2 phân số cùng mẫu số)

Nên 1-10/25  < 1-13/25

Vậy 13/15<12/25

làm 1 ý thôi

a)10/13>11/12

b)11/49<13/47

Ta co:

   12/25 = 24/50 < 24/49 < 25/49

   => 12/25 < 25/49

12/25 > 25/49

\(\dfrac{58}{21}=2\dfrac{16}{21}=2+\dfrac{16}{21}=2+\left(1-\dfrac{5}{21}\right)=3-\dfrac{5}{21}\)

\(\dfrac{61}{22}=2\dfrac{17}{22}=2+\dfrac{17}{22}=2+\left(1-\dfrac{5}{22}\right)=3-\dfrac{5}{22}\)

Ta có

\(\dfrac{5}{21}>\dfrac{5}{22}\Rightarrow3-\dfrac{5}{21}< 3-\dfrac{5}{22}\Rightarrow\dfrac{58}{61}< \dfrac{61}{22}\)

a: \(\frac{23}{35}<\frac{23,1}{35}=0,66\)

\(0,66=\frac{20,46}{31}<\frac{21}{31}\)

Do đó: \(\frac{23}{35}<\frac{21}{31}\)

b: \(\frac{-17}{24}<\frac{-16}{24}=\frac{-2}{3}\)

\(\frac{-2}{3}=\frac{-13}{19,5}<\frac{-13}{28}\)

Do đó: \(-\frac{17}{24}<-\frac{13}{28}\)

c: \(\frac{9}{16}>\frac{8}{16}=\frac12;\frac12=\frac{12}{24}>\frac{11}{24}\)

Do đó: \(\frac{9}{16}>\frac{11}{24}\)

<

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ta có 12/49 < 12/47 ( cùng tử số nên phân số nào có mẫu số bé hơn thì lớn hơn)

Mà 12/47 < 13/47

Suy ra 12/49<13/47

ta thấy 12/49 < 12/47 ;  <  12/47 < 13/47

suy ra : 12/49 < 13/47

\(a,\dfrac{2021}{2020}>1;\dfrac{8954}{88939}< 1\\ nên:\dfrac{8954}{88939}< 1< \dfrac{2021}{2020}\\ Vậy:\dfrac{2021}{2020}>\dfrac{8954}{88939}\)

\(b,\dfrac{14}{21}=\dfrac{14:7}{21:7}=\dfrac{2}{3}\\ \dfrac{51}{85}=\dfrac{51:17}{85:17}=\dfrac{3}{5}\\ Ta.có:\dfrac{2}{3}=\dfrac{10}{15};\dfrac{3}{5}=\dfrac{9}{15}\\ Vì:\dfrac{10}{15}>\dfrac{9}{15}\Rightarrow\dfrac{2}{3}>\dfrac{3}{5}\\ Vậy:\dfrac{14}{21}>\dfrac{51}{85}\)