phần mik gửi vừa nãy là vt nhầm , nên mik gửi lại

7 × 3 mu x + 20 × 3 mu x = 3 mu 25

(-50).(-12) = 600

a) 125 x 45 + 45 x 25 + 90 x 25

  =125 x 45 + 45 x 25 + 2 x 45 x 25

  =45 x [125 + 25 + ( 2 x 25 )]

  =45 x [125 + 25 + 50]

  =45 x 200

  = 9000

c) 25 x 20 x 4 - 200 x 40

  =25 x 2 x 10 x 4 - 200 x 40

  =(25 x 2 x 4) x 10 - 200 x 40

  =200 x 10 - 200 x 40

  =200 x (10 - 40)

  =200 x (-30)

  = -6000

Phần a bạn đúng rồi còn phần c sai rồi

Đề bài : \(\dfrac{97}{20}\times\left(\dfrac{25}{8}-\dfrac{221}{200}\right)< x< \dfrac{91}{10}\times\left(\dfrac{137}{20}+\dfrac{11}{4}\right)\)

\(\dfrac{97}{20}\times\left(\dfrac{25}{8}-\dfrac{221}{200}\right)=\dfrac{97}{20}\times\dfrac{101}{50}=\dfrac{9797}{1000}\)

\(\dfrac{91}{10}\times\left(\dfrac{137}{20}+\dfrac{11}{4}\right)=\dfrac{91}{10}\times\dfrac{48}{5}=\dfrac{2184}{25}=\dfrac{2184\times40}{25\times40}=\dfrac{87360}{1000}\)

\(\Rightarrow\dfrac{9797}{1000}< x< \dfrac{87360}{1000}\)

Vậy \(x\in\left(\dfrac{9797}{1000};\dfrac{87360}{1000}\right)\)

\(\left(-300\right):20+5.\left(3x-1\right)=25\)

\(\Rightarrow-15+15x-5=25\)

\(\Rightarrow-20x+15x=25\)

\(\Rightarrow15x=45\)

\(\Rightarrow x=3\)

( - 300 ) : 20 + 5( 3x -1 ) = 25 

- 15 + 5( 3x -1 ) = 25

-15 + 15x -5 = 25

- 20 + 15x = 25

15x - 20 = 25

15x - 20 + 20 = 25 + 20

15x = 25 + 20

15x = 45

15x : 15 = 45 : 15

x = 45 : 15

x = 3 

vậy x = 3

a, 515 = 500 + 15                         b, 150 + 50 < 200 + 20

    52 + 100 > 100 + 25                      147 +47 > 200 - 46

C

A