Học sinh nhẩm và ghi kết quả như sau:

200 x 2 = 400

200 x 4 = 800

100 x 5 = 500

300 x 2 =600

400 x 2 =800

500 x 1 =500

200 x 2 = 400          300 x 2 =600

200 x 4 =  800         400 x 2 =800

100 x 5 = 500          500 x 1 =500

500 + x = 100 + 500

500 + x = 600

          x = 600 - 500

          x = 1001

300 - x = 300 + 200

300 - x = 500

         x = 300 - 500

         x = -200

400 - x = 200 + 400

400 - x = 600

         x = 400 - 600

         x = -200

k mk nha mk k l

ại ^_^

500 + 100 = 100 + 500

300 + 200 =  300 + 200

400 + 200  = 200 + 400

500+x=100+500

vay x =100

300-x=300+200

vay x= - 200

400-x=200+400

vay x= -200

`@` `\text {Ans}`

`\downarrow`

`a,`

`x - 280 \div 35 = 554`

`=> x - 8 = 554`

`=> x = 554 + 8`

`=> x = 562`

Vậy, `x = 562`

`b,`

`x + (5 \div 3) = 500`

`=> x + 5/3 = 500`

`=> x = 500 - 5/3`

`=> x = 1495/3`

Vậy, `x = 1495/3`

`c,`

`390 \div (5x - 5) = 39`

`=> 5x - 5 = 390 \div 39`

`=> 5x - 5 = 10`

`=> 5x = 10 + 5`

`=> 5x = 15`

`=> x = 15 \div 5`

`=> x = 3`

Vậy, `x = 3`

`d,`

`34x - 14x = 200`

`=> (34 - 14)x = 200`

`=> 20x = 200`

`=> x = 200 \div 20`

`=> x = 10`

Vậy, `x = 10.`

`@` `\text {Kaizuu lv uuu}`

a) \(x-280:35=554\)

\(x-8=554\)

\(x=562\)

b) \(x+\left(5:3\right)=500\)

\(x+\dfrac{5}{3}=500\)

\(x=500-\dfrac{5}{3}=\dfrac{1500}{3}-\dfrac{5}{3}=\dfrac{1495}{3}\)

c) \(390:\left(5x-5\right)=39\)

\(5x-5=\dfrac{39}{390}=\dfrac{1}{10}\)

\(5x=5+\dfrac{1}{10}\)

\(5x=\dfrac{51}{10}\)

\(x=\dfrac{51}{10}.\dfrac{1}{5}=\dfrac{51}{50}\)

d) \(34x-14x=200\)

\(20x=200\)

\(x=200:20=10\)

x+200=400

x        =400-200

x        =200

x+200=500-200

x+200=300

x        =300-200

x        =100

Chúc bạn học tốt!

sai đề à

Nhók Bạch Dương

Tìm x 

x + 200 = 400

x           = 400 - 200

x           = 200

x + 200 = 500 - 200

x + 200 = 300 

x           = 300 - 200 

x           = 100 

100x200+200x500+200x400

=20000+100000+80000

=120000+80000

=200000

100 x 200 + 200 x 500 + 200 x 400

= 200 x ( 100 + 500 + 400 )

= 200 x 1000

= 200000

100x200+200x500+200x400

=20000+100000+80000

=120000+80000

=200000

a, Ta có: x ∈ B(5) = {0;5;10;15;20;25;...}

Mà x < 20 => x ∈ {0;5;10;15}

b, Ta có: x ⋮ 24; x ⋮ 45 => x ∈ BC{24;45}

24 = 2 3 . 3 ; 45 = 3 2 . 5 => BCNN(24;45) =  2 3 . 3 2 . 5 = 360

=> BC(24;45) = B(360) = {0;360;720;...}

Mà 200 < x < 500 => x = 360

c, Ta có:

452 = px+32 => 420 ⋮ x

321 = qx+21 => 320 ⋮ x

=> x ∈ ƯC(420;320)

420 =  2 2 . 3 . 5 . 7

320 =  2 6 . 5

=> ƯCLN(420;320) = 20 =  2 2 . 5

=> ƯC(420;320) = Ư(20) = {1;2;4;5;10;20}

Vậy x ∈ {1;2;4;5;10;20}

a) 6000 : 2 > 2999

b) 3000 : 3 = 200 × 5

c) 3500 : 5 < 4000 : 5

a) x= -300 -100

x = -400

b) x= -300 +100

x= -200 

1)x+100=200-500

x+100=-300

x=-300-100

x=-400

2)x-100=200-500

x-100=-300

x=-300+100

x=-200

\(x+100=200-500\)

\(x+100=-300\)

\(x=-300-100\)

\(x=-400\)

\(x-100=200-500\)

\(x-100=-300\)

\(x=-300+100\)

\(x=-200\)

x + 200 = 500 + 500

x + 200 = 1000

x           = 1000 - 200

x          = 800

Vậy x = 800

x + 200 = 500 + 500

x + 200 = 1000

x          = 1000 - 200

x          = 800

x + 200 = 500 + 500

x + 200 = 1000

          x = 1000 - 200

           x = 800