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

x=100

x+20=140-40

x+20=100

x=100-20

x=80

sai

đúng rồi bn

Sai rùi 

SỬA

140:(x-8)=7

x-8=140:7

x-8=20

x=20+8

x=28

140 - 0,5 x 40 x 5 x 0,2 x 20 x 0,25 - 40

= (140 - 40 ) - (0,5x20) x (40 x 0,25)

= 100 - 100

= 0 

140 - 0,5 x 40 x 5 x 0,2 x 20 x 0,25 - 40

= (140 - 40 ) - (0,5x20) x (40 x 0,25)

= 100 - 100

= 0 

\(\left(x-20\right):\left(x-10\right)=\left(x+140\right):\left(x+70\right)\text{ hay }\frac{x-20}{x-10}=\frac{x+140}{x+70}\)

\(\text{Áp dụng tính chất của dãy tỉ số bằng nhau ta có:}\)

\(\frac{x-20}{x-10}=\frac{x+140}{x+70}=\frac{x-20-\left(x+140\right)}{x-10-\left(x+70\right)}=\frac{x-20-x-140}{x-10-x-70}=\frac{-160}{-80}=2\)

\(\text{Suy ra:}\frac{x-20}{x-10}=2\Rightarrow x-20=2.\left(x-10\right)\)

\(x-20=2x-20\)

\(x-2x=-20+20\)

\(-x=0\)

\(x=0\)

x=0              

15 ( x - 1 ) + 20 ( x - 1 ) = 140

=> ( x - 1 ) ( 15 + 20 ) = 140

=> ( x - 1 ) . 35 = 140

=> x - 1 = 4

=> x = 5

giải luôn nhé:

(x-1)(15+20)=140

(x-1)35=140

x-1=140-35

x-1=105

x=105+1

x=105

Vậy x=106

x=106 nhé, mik ghi nhầm bn ạ

x=10

140 : ( x - 4 ) = 20 

         x - 4 = 140 : 20

         x - 4 = 7

             x = 7 + 4 

             x = 11

140 : ( x - 4 ) = 20

          x - 4   = 140 : 20

          x - 4   = 7

          x        = 7 + 4

          x        = 11