a)\(x+\dfrac{2}{3}x\dfrac{5}{6}=7\)

\(x+\dfrac{10}{18}=7\)

\(x=7-\dfrac{10}{18}\)

\(x=\dfrac{58}{9}\)

b)\(9-xx\dfrac{1}{2}=\dfrac{3}{4}\)

\(xx\dfrac{1}{2}=9-\dfrac{3}{4}\)

\(xx\dfrac{1}{2}=\dfrac{33}{4}\)

\(x=\dfrac{33}{4}:\dfrac{1}{2}\)

\(x=\dfrac{33}{2}\)

c)\(18-x:\dfrac{2}{3}=\dfrac{4}{5}-\dfrac{1}{10}\)

\(18-x:\dfrac{2}{3}=\dfrac{7}{10}\)

\(x:\dfrac{2}{3}=18-\dfrac{7}{10}\)

\(x:\dfrac{2}{3}=\dfrac{173}{10}\)

\(x=\dfrac{173}{10}x\dfrac{2}{3}\)

\(x=\dfrac{173}{15}\)

\(\frac{x+x.1}{3}:\frac{2}{9}+\frac{2}{7}=252\)

\(\Rightarrow\frac{2x}{3}:\frac{2}{9}+\frac{2}{7}=252\)

\(\Rightarrow\frac{2x}{3}:\frac{2}{9}=\frac{1762}{7}\)

\(\Rightarrow\frac{2x}{3}=\frac{3524}{63}\)

\(\Rightarrow2x=\frac{3524}{21}\)

\(\Rightarrow x=\frac{1762}{21}\)

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a)\(\frac{5}{9}\times x-1=\frac{8}{9}\)

\(\frac{5}{9}\times x=\frac{8}{9}+1\)

\(\frac{5}{9}\times x=\frac{17}{9}\)

\(x=\frac{17}{9}:\frac{5}{9}\)

\(x=\frac{17}{5}\)

b)\(x+x\times\frac{1}{3}:\frac{2}{9}+x:\frac{2}{7}=252\)

\(x+x\times\frac{3}{2}+x:\frac{2}{7}=252\)

\(x.1+x.\frac{3}{2}+x.\frac{7}{2}=252\)

\(x\left(1+\frac{3}{2}+\frac{7}{2}\right)=252\)

\(x\times6=252\)

\(x=252:6\)

\(x=42\)

\(x+x\times\dfrac{1}{4}:\dfrac{2}{7}+x:\dfrac{2}{9}=255\)

\(x+x\times\dfrac{7}{8}+x\times\dfrac{9}{2}=255\)

\(x\times\left(1+\dfrac{7}{8}+\dfrac{9}{2}\right)=255\)

\(x\times\dfrac{51}{8}=255\)

\(x=255:\dfrac{51}{8}\)

\(x=255\times\dfrac{8}{51}\)

\(x=40\)

\(x+x\times\dfrac{1}{4}:\dfrac{2}{7}+x:\dfrac{2}{9}=255\)

\(x+x\times\dfrac{7}{8}+x\times\dfrac{9}{2}=255\)

\(x+\left(1+\dfrac{7}{8}+\dfrac{9}{2}\right)=255\)

\(x\times\dfrac{51}{8}=255\)

\(x=255:\dfrac{51}{8}\left(255\times\dfrac{8}{51}\right)\)

\(x=40\)

tk cho mk nhé

x + x * 1/4 : 2/7 + x : 2/9 = 255

x + x * 1/4 * 7/2 + x * 9/2 = 255

x + x * 7/8 + x * 9/2 = 255

x * ( 1 + 7/8 + 9/2 ) = 255

x * (8/8 + 7/8 + 36/8 ) = 255

x * 51/8 = 255

x = 255 : 51/8

x = 255* 8/51

x = 40

Chúc bạn học tốt!

x + x × 1/4 : 2/7 + x : 2/9 = 255

x + x × 1/4 × 7/2 + x × 9/2 = 255

x + x × 7/8 + x × 9/2 = 255

x × (1 + 7/8 + 9/2) = 255

x × (8/8 + 7/8 + 36/8) = 255

x × 51/8 = 255

x = 255 : 51/8

x = 255 × 8/51

x = 40

x + x × 1/4 : 2/7 + x : 2/9 = 255

x + x × 1/4 × 7/2 + x × 9/2 = 255

x + x × 7/8 + x × 9/2 = 255

x × (1 + 7/8 + 9/2) = 255

x × (8/8 + 7/8 + 36/8) = 255

x × 51/8 = 255

x = 255 : 51/8

x = 255 × 8/51

x = 40

x + x × 1/4 : 2/7 + x : 2/9 = 255

x + x × 1/4 × 7/2 + x × 9/2 = 255

x + x × 7/8 + x × 9/2 = 255

x × (1 + 7/8 + 9/2) = 255

x × (8/8 + 7/8 + 36/8) = 255

x × 51/8 = 255

x = 255 : 51/8

x = 255 × 8/51

x = 40

Vậy x = 40

Lời giải:

$x+x\times \frac{1}{4}: \frac{2}{7}+x: \frac{2}{9}=255$

$x+x\times \frac{7}{8}+x\times \frac{9}{2}=255$

$x\times (1+\frac{7}{8}+\frac{9}{2})=255$

$x\times \frac{51}{8}=255$

$x=255: \frac{51}{8}=40$

\(\dfrac{3}{2}\times\dfrac{4}{5}-x=\dfrac{2}{3}\)

\(\dfrac{6}{5}-x=\dfrac{2}{3}\)

\(x=\dfrac{6}{5}-\dfrac{2}{3}\)

\(x=\dfrac{8}{15}\)

-------------------------------------

\(x+x\times\dfrac{7}{8}+x\times\dfrac{9}{2}=255\)

\(x\times\left(1+\dfrac{7}{8}+\dfrac{9}{2}\right)=255\)

\(x\times\dfrac{51}{8}=255\)

\(x=255:\dfrac{51}{8}\)

\(x=40\)

x là dấu nhân còn X là X ạ   gấp 

\(x+x.\frac{1}{4}:\frac{2}{7}+x:\frac{2}{9}=255\) 

\(\Leftrightarrow x+x\frac{1}{4}.\frac{7}{2}+x.\frac{9}{2}=255\)   

\(\Leftrightarrow x\left(1+\frac{1}{4}.\frac{7}{2}+\frac{9}{2}\right)=255\)

\(\Leftrightarrow x.\frac{51}{8}=255\) 

\(\Leftrightarrow x=40\)