a) 115 + 5 ( x – 4 ) = 120

5 ( x – 4 ) = 120 – 115

5 ( x – 4 ) = 5

x – 4 = 5 : 5

x – 4 = 1

x = 1 + 4

x = 5

b)  5|x| –  10 0 = 3 7 : 3 5

5| x | – 1 =  3 2

5| x | = 9 + 1

5| x | = 10

| x | = 2

x = 2 hoặc x = -2

c)  2 2016 . 2 x - 1 = 2 2015

2 x - 1 = 2 2015 :   2 2016

2 x - 1 = 2 2015 - 2016

2 x - 1 = 2 - 1

⇒ x – 1 = -1

x = -1 + 1

x = 0

Ta có:

\(115+5\left(x-4\right)=120\)

\(5\left(x-4\right)=120-115=5\)

\(\Rightarrow x-4=1\Rightarrow x=5\)

115+5(x-4)=120

5(x-4)=120-115

5(x-4)=5

x-4=5:5

x-4=1

x =1+4

x =5

=>5 (x-4)=120-115

=>5 (x-4)=5

=>x-4 =1

=>x =5

Bài 2: 

a: 4x+320=480

=>4x=160

hay x=40

b: 150-x:7=120

=>x:7=30

hay x=210

=>x+120=165-65-115

=>x+120=-115

hay x=-235

`@` `\text {Ans}`

`\downarrow`

`a)`

\(24 \div a+24=30\)

`=> 24 \div a = 30 - 24`

`=> 24 \div a = 6`

`=> a = 24 \div 6`

`=> a = 4`

Vậy, `a=4`

`b)`

\( 1974 \div 14+a \times 141=423\)

`=> 141 + a \times 141 = 423`

`=> a \times 141 = 423 - 141`

`=> a \times 141 = 282`

`=> a = 282 \div 141`

`=> a = 2`

Vậy, `a=2`

`c)`

\(120-(45-a \times 4)=115\)

`=> 45 - a \times 4 = 120 - 115`

`=> 45 - a \times 4 = 5`

`=> a \times 4 = 45 - 5`

`=> a \times 4 = 40`

`=> a = 40 \div 4`

`=> a = 10`

Vậy, `a=10`

`d)`

\((a \times 4-44) \div 4=44\)

`=> a \times 4 - 44 = 44 \times 4`

`=> a \times 4 - 44 = 176`

`=> a \times 4 = 176 + 44`

`=> a \times 4 = 220`

`=> a = 220 \div 4`

`=> a = 55`

Vậy, `a = 55.`

a) 24:a+24=30

 24:a= 30 - 24

24:a=6

a= 24:6

a=4

______

b) 1974:14+ax141=423 

141 + a x 141 = 423

141 x (a+1) = 423

a+1 = 423 : 141

a+1=3

a=3-1

a=2

_____
c) 120-(45-ax4)=115

45 - a x 4= 120 - 115

45 - a x 4= 5

a x 4 = 45 - 5

a x 4 = 40

a = 40:4

a=10

______

  d) (ax4-44):4=44

a x 4 - 44 = 44  x 4

a x 4 - 44 = 176

a x 4 = 176 + 44

a x 4 = 220

a= 220:4

a=55

a) \(24:a+24=30\)

\(\Rightarrow24:a=30-24\)

\(\Rightarrow24:a=6\)

\(\Rightarrow a=24:6\)

\(\Rightarrow a=4\)

b) \(1974:14+a\cdot141=423\)

\(\Rightarrow141+a\cdot141=423\)

\(\Rightarrow141\cdot\left(1+a\right)=423\)

\(\Rightarrow1+a=423:141\)

\(\Rightarrow1+a=3\)

\(\Rightarrow a=3-1\)

\(\Rightarrow a=2\)

c) \(120-\left(45-a\cdot4\right)=115\)

\(\Rightarrow45-a\cdot4=120-115\)

\(\Rightarrow45-a\cdot4=5\)

\(\Rightarrow a\cdot4=45-5\)

\(\Rightarrow a=40:4\)

\(\Rightarrow a=10\)

d) \(\left(a\cdot4-44\right):4=44\)

\(\Rightarrow a\cdot4-44=44\cdot4\)

\(\Rightarrow a\cdot4-44=176\)

\(\Rightarrow a\cdot4=176+44\)

\(\Rightarrow a\cdot4=220\)

\(\Rightarrow a=220:4\)

\(\Rightarrow a=55\)

a,(x+1)(x-20)=0

  =>x+1=0 va x-20=0

=>x=-1 va x=20

a, X=-1;x=20.

b,x=-147

c,x=-110

Đáp án cần chọn là: B

2 x − 3 4 − 4 15 − 1 4 = 1 20 − 1 15 2 x − 3 4 − 1 60 = − 1 60 2 x − 3 4 = 0 2 x − 3 4 = 0 2 x = 3 4 x = 3 8

Vậy có 1 giá trị của x thỏa mãn bài toán.