tính nhanh + tìm x ạ: a) 6 x (15 + 5x) = 300 b) 64x + 36x = 3 600 c) (24 x 15 - x) : 1/4 = 400 d) 3 200 : (8 + 3x) = 4 e) 6 x (2 800 - 8x) = 7 200 f) 16,6x - 6,6x = 166 b) 6,28 x 15,68 + 15,68 x 3,72 c) 40 x 0,25 x 612,8 d) 36,2 x 101 - 36 - 0,2 e) 1 112,48 x 3,47 - 3,47 x 112,48

a) `6 x (15 + 5x) = 300`

`6 x (15 + 5x) = 300`

`15 + 5x = 300 : 6`

`15 + 5x = 50`

`5x = 50 - 15`

`5x = 35`

`x = 35 : 5`

`x = 7`

b) `64x + 36x = 3 600`

`64x + 36x = 3 600`

`x(64 + 36) = 3 600`

`100x = 3 600`

`x = 3 600: 100`

`x = 36`

c)` (24 x 15 - x) : 1/4 = 400`

`(24 x 15 - 2x) : 1/4 = 400`

`24 x 15 - 2x = 400 x 1/4`

`24 x 15 - 2x = 100`

`360 - 2x = 100`

`2x = 360 - 100`

`2x = 260`

`x = 260 : 2`

`x = 130`

d)` 3 200 : (8 + 3x) = 4`

`3 200 : (8 + 3x) = 4`

`8 + 3x = 3 200 : 4`

`8 + 3x = 800`

`3x = 800 - 8`

`3x = 792`

`x = 792 : 3`

`x = 264`

e) `6 x (2 800 - 8x) = 7 200`

`6 x (2 800 - 8x) = 7 200`

`2 800 - 8x = 7 200 : 6`

`2 800 - 8x = 1 200`

`8x = 2 800 - 1 200`

`8x = 1 600`

`x = 1 600 : 8`

`x = 200 `

f) `16,6x - 6,6x = 166`

`16,6x - 6,6x = 166`

`x. (16,6 - 6,6) = 166`

`x . 10 = 166`

`x = 166 : 10`

`x = 16,6`

b) `6,28 x 15,68 + 15,68 x 3,72`

`6,28 x 15,68 + 15,68 x 3,72`

`= 15,68 x (6,28 + 3,72)`

`= 15,68 x 10`

`= 156,8`

c)` 40 x 0,25 x 612,8`

`40 x 0,25 x 612,8`

`= (40 x 0,25) x 612,8`

`= 10 x 612,8`

`= 6 128`

d) `36,2 x 101 - 36 - 0,2`

`36,2 x 101 - 36 - 0,2`

`= 36,2 x 101 - (36 + 0,2)`

`= 36,2 x 101 - 36,2`

`= 36,2 x (101 - 1)`

`= 36,2 x 100`

`= 3 620`

e) `1 112,48 x 3,47 - 3,47 x 112,48  `

`1 112,48 x 3,47 - 3,47 x 112,48`

`= 3,47 x (1 112,48 - 112,48)`

`= 3,47 x 1 000`

`= 3 470`

@Doraenin

~~ Xin hn nếu vừa ý bạn ạ ~~