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

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

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

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

Bài 3: 

a: =>x=13-24=-11

b: =>3x=12

hay x=4

13 +  x/20 = 3/4 

        x/20 = 3/4 - 13 

        x/20 = -49/4

   => x = - 49 x 20 / 4 

        x =  - 245

cái này là theo  ý kiến mk nhá ! 

tk ủng hộ mk nhé !!!!!!

Câu 1 sai đề.

Câu 2:

\(23-\frac{x}{25}=\frac{4}{5}\)

\(\frac{x}{25}=\frac{111}{5}\)

\(x=555\)

Câu 2:

$23-\frac{x}{25}=\frac{4}{5}$

$\frac{x}{25}=\frac{111}{5}$

$x=555$

`(13+x)/20 = 3/4`

`(13+x) xx4=3xx20`

`(13+x)xx4=60`

`13+x=60:4`

`13+x=15`

`x=15-13`

`x=2`

__

`(23-x)/25 =4/5`

`(23-x)xx5=4xx25`

`(23-x)xx5=100`

`23-x=100:5`

`23-x=20`

`x=23-20`

`x=3`

BÀI 1: Tính

1) -(-10)-(+14)=10-14=-4

2) -(+15)-12=-15-12=-27

3) (-11)-(-13)=-11+13=2

4) -(-13)-(-10)=13+10=23

5) -4-(+7)=-4-7=-11

Bài 2 : tìm x:

a)x+(-5)=-(-7) 

           x=7+(-5)

           x=2

vậy x=2

b)x-8=-(+10)

x-8=10

   x=10+8

  x=18

vậy x=18

c)x-(-12)=14

x+12=14

      x=14-12

      x=2

vậy x=2

d)x-(+3)=-17

x-3=17

   x=17+3

   x=20

vậy x=20

e)x+20=-(-23)

x+20=23

      x=23-20

      x=3

vậy x=3

BÀI 3:tính

a)17-(-9)-(+25)

=17+9-25

=26-25

=1

b)-[-13]-15+(-20)

=13-15-20

=-2-20

=-22

c)-17-(-16)-23

=-17+16-23

=-1-23

=-24

d)-(-25)-(-14)+(-17)

=25+14-17

=39-17

=22

cảm ơn bạn rất nhiều chúc bạn và gia đình mạnh khỏe, vui vẻ bên nhau và cùng đón 1 cái TẾT vui vẻ!

HAPPY NEW YEAR

haha ối giời ơi

2x+20=-22

=> 2x = -22 - 20

=> 2x = -42

=> x = -42 : 2

=> x = -21

Vậy x = -21

2x+20=-22

2x=-22-20

2x=-42

  x=-42:2

  x=-21

-(-30)-(-x)=13

30+x=13

      x=13-30

      x=-17

-(-x)+14=12

x+14=12

      x=12-14

      x=-2

x+20=-(-23)

x+20=23

      x=23-20

      x=3

15-x+17=-(-6)+|-12|

15+17+x=6+12

32+x=18

      x=18-32

      x=-14

-|-5|-(-x)+4=3-(-25)

-5+x+4=3+25

-5+4+x=28

-1x=28

   x=28:(-1)

   x=-28

cam on moi nguoi nhe

a) \(\frac{13+x}{20}=\frac{3}{4}\)

\(\Rightarrow\frac{13+x}{20}=\frac{15}{20}\)

\(\Rightarrow13+x=15\)

\(\Rightarrow\)        \(x=15-13\)

\(\Rightarrow\)\(x=2\)

b)\(\frac{23-x}{25}=\frac{4}{5}\)

\(\Rightarrow\frac{23-x}{25}=\frac{20}{25}\)

\(\Rightarrow23-x=20\)

\(\Rightarrow\)        \(x=23-20\) 

\(\Rightarrow\)        \(x=3\)

a, 13+x/20= 3/4

Suy ra: ( 13+x). 4= 20.3

Suy ra: (13+x).4=60

Suy ra: 13+x=60:4

Suy ra: 13+x=15

Suy ra: x=15-13

Suy ra: x=2

Vậy x=2

a\(\frac{13+x}{20}=\frac{3}{4}\Rightarrow\left(13+x\right)\times4=20\times3\)

\(\left(13+x\right)\times4=60\)

\(13+x=60:4=15\)

\(x=15-13=2\)

Vậy x=2

b,\(\frac{23-x}{25}=\frac{4}{5}=\left(23-x\right)\times5=25\times4\)

\(\left(23-x\right)\times5=100\Rightarrow23-x=100:5=20\)

\(x=23-20=3\)

Vậy x = 3

13+\(\frac{x}{20}\)=\(\frac{3}{4}\)

=>\(\frac{x}{20}\)=\(\frac{3}{4}-13\)

=>\(\frac{x}{20}=\frac{3}{4}-\frac{52}{4}=-\frac{49}{4}=-\frac{245}{20}\)

=>x=-245

\(23-\frac{x}{25}=45\)

\(=>\frac{x}{25}=23-45=-22=-\frac{550}{25}\)

=>x=-550

X/20 =3/4 — 13

X/20 = —49/4

=» x= —9.8