-2x + 0,25 = -x - 0,5

0,25 + 0,5 = -x + 2x

0,75 = x 

Vậy x = 0,75

-2x + 0,25 = -x-0,5
-2x + x       = -0,5 - 0,25
-x               = -0,75
 x               = 0,75
           Vậy x = 0,75

Số tiền mẹ An phải trả là:

   (8000000 + 300000) x (100% - 20%) = 6640000 (đồng)

\(\dfrac{2}{5}x-\dfrac{1}{5}=-0,6\\ =>\dfrac{2}{5}x-\dfrac{1}{5}=-\dfrac{3}{5}\\ =>\dfrac{2}{5}x=-\dfrac{3}{5}+\dfrac{1}{5}\\ =>\dfrac{2}{5}x=-\dfrac{2}{5}\\ =>x=-\dfrac{2}{5}:\dfrac{2}{5}\\ =>x=-1\)

2/5x - 1/5 = -0,6

2/5x - 1/5 = -3/5

2/5x         = -3/5 + 1/5

2/5x         = -2/5

    x          = -2/5 : 2/5

    x          = -10/10 = -1

2⁷ x 9² x 2022⁰/3⁵ x 8²

= 2⁷ x 3⁴ x 1/3⁵ x 2⁶

= 2/3

mn giúp mình vời, mình cần gấp
 

1/2 + 3/4 . (x + 5) = 4/3
1/2 + (x + 5 ) = 4/3 : 3/4
1/2 + (x + 5) = 16/9
x + 5 = 16/9 - 1/2 
x + 5 = 23/18
x      = 23/18 - 5 
x = tự tính lười quá :)

1/2 + 3/4(x+5) = 4/3

3/4(x+5) = 1/2-4/3

3/4(x+5) =5/6

x+5 = 5/6÷3/4

x+5=10/9

x= -35/9

Ta có:

\(D=2021-\dfrac{1}{4}-\dfrac{2}{5}-\dfrac{3}{6}-...-\dfrac{2021}{2024}\\ =\left(1-\dfrac{1}{4}\right)+\left(1-\dfrac{2}{5}\right)+\left(1-\dfrac{3}{6}\right)+...+\left(1-\dfrac{2021}{2024}\right)\\ =\dfrac{3}{4}+\dfrac{3}{5}+\dfrac{3}{6}+...+\dfrac{3}{2024}\\ =3\left(\dfrac{1}{4}+\dfrac{1}{5}+\dfrac{1}{6}+...+\dfrac{1}{2024}\right)\)

\(E=\dfrac{1}{20}+\dfrac{1}{25}+...+\dfrac{1}{10120}\\ =\dfrac{1}{4.5}+\dfrac{1}{5.5}+...+\dfrac{1}{2024.5}\\ =\dfrac{1}{5}\left(\dfrac{1}{4}+\dfrac{1}{5}+...+\dfrac{1}{2024}\right)\)

Dễ thấy 

\(3\left(\dfrac{1}{4}+\dfrac{1}{5}+\dfrac{1}{6}+...+\dfrac{1}{2024}\right)>\dfrac{1}{5}\left(\dfrac{1}{4}+\dfrac{1}{5}+...+\dfrac{1}{2024}\right)\\ \Rightarrow D>E\)