Câu 4: \(\left(-\frac13-\frac25\right)\cdot x+0,12=-0,38\)

=>\(x\left(-\frac{5}{15}-\frac{6}{15}\right)=-0,38-0,12=-0,5=-\frac12\)

=>\(x\cdot\frac{-11}{15}=\frac{-1}{2}\)

=>\(x=\frac12:\frac{11}{15}=\frac12\cdot\frac{15}{11}=\frac{15}{22}\)

Câu 3: Số mét vải loại II có thể mua được là:

270:90%=300(m)

ko bt lm

ĐKXĐ: x∉{0;-2}

Ta có; \(\frac{270}{x+2}+\frac{7}{10}=\frac{270}{x}\)

=>\(\frac{270}{x}-\frac{270}{x+2}=\frac{7}{10}\)

=>\(\frac{270\left(x+2\right)-270x}{x\left(x+2\right)}=\frac{7}{10}\)

=>\(\frac{270x+540-270x}{x\left(x+2\right)}=\frac{7}{10}\)

=>7x(x+2)=5400

=>\(7x^2+14x-5400=0\)

=>\(x^2+2x-\frac{5400}{7}=0\)

=>\(x^2+2x+1-\frac{5407}{7}=0\)

=>\(\left(x+1\right)^2=\frac{5407}{7}\)

=>\(x+1=\pm\sqrt{\frac{5407}{7}}\)

=>\(x=-1\pm\sqrt{\frac{5407}{7}}\) (nhận)

a, x - 140 : 35= 270

x - 4 = 270

x = 274

b, (x - 140) : 35= 270

x - 140 = 9450

x = 9590

$\frac{270}{x-12}-\frac{270}{x}=\frac{2}{3}$

\(\Leftrightarrow-2x^2+24x+9720=0\)

\(\Leftrightarrow2x^2-24x-9720=0\)

\(\Leftrightarrow\left[{}\begin{matrix}x_1=6+12\sqrt{34}\\x_2=6-12\sqrt{34}\end{matrix}\right.\) \(\left(tmđk\right)\)

270*20+58*270+28*270=270*/20+58+28\=270*100=270 

Tìm x : 

x + 1/3 = 4/5 

x = 4/5 - 1/3 

x = 12/15 - 5/15 

x = 7/15 

x - 1/2 = 2/7 

x = 2/7 + 1/2 

x = 4/14 + 7/14 

x = 11/14 

4/7 × x = 1/3 

x = 1/3 : 4/7 

x = 1/3 × 7/4 

x = 7/12 

x : 2/5 = 2/9 

x = 2/9 × 2/5 

x = 4/45 

20 × 7 : ( 5 × x - 3 × 5 ) = 4 

140 : 5  × ( x - 3 )  = 4 

5 × ( x - 3 ) = 140 : 4 

5 × ( x - 3 ) = 35 

x - 3 = 35 : 5 

x - 3 = 7 

x = 7 + 3 

x = 10 

x - 270  = 420 : 105 

x - 270 = 4 

x = 4 + 270 

x = 274 

x - 140 : 35 = 270 

x - 4 = 270 

x  = 270 + 4 

x = 274 

x + 1/3 = 4/5

x           = 4/5 - 1/3 

x           =  7/15

x - 1/2 = 2/7

x         = 2/7 + 1/2

x        = 11/14

4/7 * x  =  1/3

        x   = 1/3 : 4/7

        x    = 7/12

x : 2/5 = 2/9

x         = 2/9 * 2/5

x          4 / 45

20 * 7 : ( 5*x - 3 * 5) =4

= 140 :(5*x -3 *5) =4

5*x- 3*5 = 140 : 4

5*x - 3 * 5 = 35 

5* x           = 35 + 3 * 5

5 * x           =  50

x                = 50 : 5

x                = 10

x - 270 = 402 : 105

x - 270 = 4

x          = 270 + 4

x           =   274

x- 140 : 35 = 270 

x -  4          = 270

x                 = 270 + 4

x                  = 274

\(\Leftrightarrow3^x\cdot10=270\)

hay x=3