a)Ta có:
\(\dfrac{90}{160}=\dfrac{90:10}{160:10}=\dfrac{9}{16}=\dfrac{9\times7}{16\times7}=\dfrac{63}{112}\)
\(\dfrac{6}{7}=\dfrac{6\times16}{7\times16}=\dfrac{96}{112}\)
\(\Rightarrow\dfrac{90}{160}< \dfrac{6}{7}\)
b)Ta có:
\(\dfrac{18}{20}=\dfrac{18:2}{20:2}=\dfrac{9}{10}\)
\(\Rightarrow\dfrac{18}{20}>\dfrac{7}{10}\)

\(a,\dfrac{90}{160}=\dfrac{9}{16}\\ MSC:112\\ \dfrac{9}{16}=\dfrac{9.7}{16.7}=\dfrac{63}{112}\\ \dfrac{6}{7}=\dfrac{6.16}{7.16}=\dfrac{96}{112}\\ 63< 96\\ =>\dfrac{90}{160}< \dfrac{6}{7}\\ b,\dfrac{18}{20}=\dfrac{9}{10}\\ 9>7\\ =>\dfrac{18}{20}>\dfrac{7}{10}\)

\(\dfrac{90}{160}=\dfrac{9}{16}\)

\(\dfrac{6}{7}=\dfrac{6.16}{7.16}=\dfrac{96}{112}\); \(\dfrac{9}{16}=\dfrac{9.7}{16.7}=\dfrac{63}{112}\)

\(\Rightarrow\dfrac{6}{7}>\dfrac{9}{16}\)

B. \(\dfrac{18}{20}=\dfrac{9}{10}\)

\(\Rightarrow\dfrac{18}{20}>\dfrac{7}{10}\)

câu trả lời là 13/40 nhé 

NHỚ

Lời giải:

$\frac{1}{3}=\frac{3}{9}$

$\frac{2}{3}=\frac{6}{9}$

Hai phân số lớn hơn 1/3 và nhỏ hơn 2/3 là: $\frac{4}{9}; \frac{5}{9}$

vì 3 số chia hết cho nhau :

nếu 1313:13 =101 thì 1313:101=13 ( Vậy 13=13)

nếu 131313:13=10101 thì 131313:10101=13 (Vậy 13=13)

         Suy ra 3 số bằng nhau

về sau tăng gấpđôi số đầu

đúng k nha

\(=\left(4x-x-1\right)\left(4x+x+1\right)=\left(3x-1\right)\left(5x+1\right)\)

\(=\left(4x-x-1\right)\left(4x+x+1\right)=\left(3x-1\right)\left(5x+1\right)\)

=(3x-1)(5x+1)