\(a.\dfrac{12+x}{42}=\dfrac{35}{42}\Leftrightarrow12+x=35\Leftrightarrow x=23\)

\(b.\dfrac{25-x}{40}=\dfrac{3}{8}\Leftrightarrow\dfrac{25-x}{40}=\dfrac{15}{40}\Leftrightarrow25-x=15\Leftrightarrow x=10\)

\(c.\dfrac{13+x}{20}=\dfrac{3}{4}\Leftrightarrow\dfrac{13+x}{20}=\dfrac{15}{20}\Leftrightarrow13+x=15\Leftrightarrow x=2\)

\(d.\dfrac{23-x}{25}=\dfrac{20}{25}\Leftrightarrow23-x=20\Leftrightarrow x=3\)

x : 5 = 13   x : 6 = 25   x : 3 = 48

x = 13 x 5   x = 25 x 6   x = 48 x 3

x = 65   x = 150   x = 144

=> vế trong ngoặc là 0 nhoa

rồi bạn thay vô tính thôi

\(2+5+3=x-3\)

\(=10=x-3\)

\(\Rightarrow x=10+3=13\)

\(5+25=x\cdot6\)

\(=30=x\cdot6\)

\(\Rightarrow x=30:6=5\)

Ủng hộ mk nka!!!^_^^_^^_^

2+5+3=x-3

  10 = x-3

x-3 = 10

x    = 10+3 = 13

5+25 = x.6

  30 = x.6

x.6 = 30

x  = 30 : 6 = 5

2 + 5 + 3 = x - 3

=> x - 3 = 2 + 5 + 3

=> x - 3 = 10

=> x      = 10 + 3

=> x      = 13

5 + 25 = x X 6

=> x X 6 = 5 + 25

=> x X 6 = 30

=> x       = 30 : 6

=> X       = 5

\(x\) \(\times\) \(\dfrac{4}{5}\) = 15

\(x\)         = 15 : \(\dfrac{4}{5}\)

\(x\)         = \(\dfrac{75}{4}\) 

\(\dfrac{12}{25}\) \(\times\) \(x\) = \(\dfrac{4}{10}\)

          \(x\) = \(\dfrac{4}{10}\) : \(\dfrac{12}{25}\)

          \(x\) = \(\dfrac{5}{6}\) 

\(\dfrac{6}{5}\): \(x\) = \(\dfrac{1}{3}\)\(x\) : \(\dfrac{2}{7}\) = \(\dfrac{3}{5}\) (xem lại đề bài)

x = 25/3 - 5/6 

x = 45/6 = 15/2( rút gọn cho 3)

Vậy x = 15/2

1: =>x=8-35=-27

2: =>15-4+x=6

=>x+11=6

hay x=-5

3: =>-30+25-x=-1

=>x+5=1

hay x=-4

4: =>x-(-13)=-8

=>x+13=-8

hay x=-21

5: =>x-29-17+38=-9

=>x-8=-9

hay x=-1

=>-2x-3/5=-5/6*8/25=-40/150=-4/15

=>-2x=-4/15+3/5=5/15=1/3

=>x=-1/6