140-100:x=20

  100:x=140-20

  100:x=120

         x=\(\dfrac{5}{6}\)

\(140-100:x=20\)

\(\Rightarrow100:x=120\)

\(\Rightarrow x=\dfrac{5}{6}\)

Ta có: 140-100:x=20

nên 100:x=120

hay \(x=\dfrac{5}{6}\)

x=100+10-5

x=105

vay x=105

và y=80

x + 5 - 10 = 100

x = 100 - 5 + 10 

x = 105

câu 2  theo mk là sai đề

y + 20 - x  = 100 - x

y + 20 = 100 (cho x = 0 hoặc bỏ x)

       x = 100 - 20

       x = 80

(x-5).3/10=2000+5

(x-5).3/10=2005

x-5=2005:3/10

x-5=2005.10/3

x-5=20050/3

x=20050/3 +5

x=20065/3

\(\left(x-5\right)\)\(.\)\(\frac{30}{100}\)\(=\)\(20\times100+5\)

\(\left(x-5\right)\)\(.\)\(\frac{3}{10}\)\(=\)\(2005\)

\(\left(x-5\right)\)\(=\)\(2005\)\(\div\)\(\frac{3}{10}\)

\(\left(x-5\right)\)\(=\)\(2005\)\(.\)\(\frac{10}{3}\)

\(\left(x-5\right)\)\(=\)\(\frac{20050}{3}\)

\(x=\frac{20055}{3}\)

Hok tốt

x=50

k mik nha

^_^

Học tốt

x-{150-[30+20.(100:20)]}=30

x={150-[30+20.5]}=30

x={150-[20+100]}=30

x={150-120}=30

x=30

Vậy x=30

x - { 150 - [30 + 20 . ( 100.20 )}} = 30

X = {150 - [30 + 20 . 5 ]} = 30

X= [150 - 130 ] = 30

X - 20 = 30 

x = 30 + 20 

X = 50

XONG RÙI K MÌNH NHA 

a) (125 - x) + 25 = 98

125 - x = 98 - 25

125 - x = 73

x = 125 - 73

x = 52

b) 100 : (x + 20) = 68 : 34

100 : (x + 20) = 2

x + 20 = 100 : 2

x + 20 = 50

x = 50 - 20

x = 30

c) (3x + 12) . 5 = 25 . 4 - 10

(3x + 12) . 5 = 100 - 10

(3x + 12) . 5 = 90

3x + 12 = 90 : 5

3x + 12 = 18

3x = 18 - 12

3x = 6

x = 6 : 2

x = 3

d) 210 : (2x - 3) - 20 = 10

210 : (2x - 3) = 10 + 20

210 : (2x - 3) = 30

2x - 3 = 210 : 30

2x - 3 = 70

2x = 70 + 3

2x = 73

x = 73/2

a, ( 125 - x ) + 25 = 98

⇒ 125 - x = 73

⇒ x = 52.

Vậy..

b, 100 : ( x + 20 ) = 68 : 34

⇒ 100 : ( x + 20 ) = 2

⇒ x + 20 = 50

⇒ x = 30

Vậy...

c, ( 3 . x + 12 ) . 5 = 25 . 4 - 10

⇒ ( 3 . x + 12 ) . 5 = 90

⇒ 3 .x + 12 = 18

⇒ 3x = 6

⇒ x = 2.

Vậy...

d, 210 : ( 2 .x - 3 ) - 20 = 10

⇒ ( 2 .x - 3 ) - 20 = 21

⇒ 2x - 3 = 41

⇒ 2x = 44

⇒ x = 22.

Vậy..

Cho mk chỉnh lại câu cuối:

 d, 210 : ( 2 .x - 3 ) - 20 = 10

⇒ 210 : ( 2 .x - 3 ) = 30

⇒ 2 . x - 3 = 7

⇒ 2x = 10

⇒ x = 5.

Vậy..

(70- 20 )* x = 100

=> 50x = 100

=> x = 100 : 50

=> x = 2Vậy x = 2 thì (70- 20 )* x = 100

20 + x - 10 = 100

20 + x = 100 + 10

20 + x = 110

        x = 110 - 20

        x = 90

20+x-10=100

20+x=100+10

20+x=110

x=110-20

x=90

20 + x - 10 = 100

20+x          =100+10

20+x          =110

x                =110-20

x                 =90

100 - x = 20

        x = 100 - 20

        x = 80

x = 100 - 20

x = 80

vậy x = 80

100-x=20

      x=100-20

      x=80