25%.x+1/2.x=12

=> 1/4.x+1/2.x=12

=> x.(1/4+1/2)=12

=> x.0,75       =12

=> x              =12:0,75

=> x              =16

Vậy x=16

25/100.x + 1/2.x = 12

1/10.x + 1/2.x =12 

(1/10 + 1/2 ).x =12

( 1/10 + 5/10 ).x =12

6/10 = 3/5.x = 12

               x = 12 : 3/5

                x = 12 . 5/3

                x = 20

\(\left(x-\frac{2}{5}\right)×\frac{1}{2}=1=>\left(x-\frac{2}{5}\right)=1:\frac{1}{2}=>\left(x-\frac{2}{5}\right)=2=>x=2+\frac{2}{5}=>x=\frac{12}{5}\)

vậy \(x=\frac{12}{5}\)

             Bài làm :

Ta có :

\(\left(x-\frac{2}{5}\right)\times\frac{1}{2}=1\)

\(x-\frac{2}{5}=1\div\frac{1}{2}\)

\(x-\frac{2}{5}=2\)

\(x=2+\frac{2}{5}=2,4\)

Vậy x=2,4

= (x - 2/5) * 1/2 =1
=x- 2/5=1:1/2
=x -2/5= 2
=x       = 2 +2/5
=x       = 12/5

\(\frac{5x+1}{2}=\frac{2}{3}\Rightarrow3\left(5x+1\right)=2\times2\)

<=>15x+3=4

=>15x=1

=>x=\(\frac{1}{15}\)

5x +1/2=2/3

5x        =2/3-1/2

5x        =4/6-3/6

5x        = 1/6

  x        =1/6:5

  x        =1/30

k mk nha

5x +1/2=2/3

5x        =2/3-1/2

5x        =4/6-3/6

5x        = 1/6

  x        =1/6:5

  x        =1/30

a, |x - 3,5| = 7,5

=> x - 3,5 = 7,5 hoặc x - 3,5 = -7,5

=> x = 11 hoặc x = -4 

vậy_

b, |x + 4/5| - 1/2 = 0

=> |x + 4/5| = 1/2

=> x + 4/5 = 1/2  hoặc x + 4/5 = -1/2

=> x = -7/10 hoặc x = -9/10

vậy_

c, 3,6 - |x - 0,4| = 0

=> |x - 0,4| = 3,6

=> x - 0,4 = 3,6 hoặc x - 0,4 = -3,6

=> x = 4 hoặc x = -3,2

vậy_

a)/x-3,5/=7,5

TH1---------x-3,5=7,5       x=7,5+3,5=11

TH2--------x-3,5=-7,5      x=-7,5+3,5=-4

vậy\(x\in\left\{11;-4\right\}\)

\(\frac{25-x}{18}=\frac{1}{2}\)

\(\frac{25-x}{18}=\frac{9}{18}\)

\(25-x=9\)

\(x=25-9\)

\(x=16\)

\(\frac{1}{2}+\frac{1}{6}+\frac{1}{12}+\frac{1}{20}+...+\frac{1}{132}\)

\(=\frac{1}{1.2}+\frac{1}{2.3}+\frac{1}{3.4}+\frac{1}{4.5}+...+\frac{1}{11.12}\)

\(=\frac{1}{1}-\frac{1}{2}+\frac{1}{2}-\frac{1}{3}+\frac{1}{3}-\frac{1}{4}+...+\frac{1}{11}-\frac{1}{12}\)

\(=\frac{1}{1}-\frac{1}{12}\)

\(=\frac{11}{12}\)

\(A=\frac{1}{2}+\frac{1}{6}+\frac{1}{12}+\frac{1}{20}+...+\frac{1}{132}\)

\(A=\frac{1}{1x2}+\frac{1}{2x3}+\frac{1}{3x4}+\frac{1}{4x5}+...+\frac{1}{11x12}\)

\(A=\frac{2-1}{1x2}+\frac{3-2}{2x3}+\frac{4-3}{3x4}+\frac{5-4}{4x5}+...+\frac{12-11}{11x12}\)

\(A=1-\frac{1}{2}+\frac{1}{2}-\frac{1}{3}+\frac{1}{3}-\frac{1}{4}+...+\frac{1}{11}-\frac{1}{12}\)

\(A=1-\frac{1}{12}=\frac{11}{12}\)

\(\frac{25-x}{18}=\frac{1}{2}\)

\(\frac{25-x}{18}=\frac{9}{18}\)

\(25-x=9\)

\(x=25-9\)

\(x=16\)

\(\frac{25-x}{18}=\frac{1}{2}\)

\(\frac{25-x}{18}=\frac{9}{18}\)

\(\Rightarrow25-x=9\)

\(x=25-9\)

\(x=16\)