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Giải thích các bước giải:

\(3/\\ a,\ (42\times 43+43\times 57+43)-360:4\\ =43\times (42+57+1)-90\\ =43\times 100-90\\ =4300-90\\ =4210\\ b,\ (372-19\times 4)-(981:9-13)\\ =(372-76)-(109-13)\\ =296-96\\ =200\\ c,\ 456:2\times 18+456:3-10\\ =456\times \dfrac12\times 18+456\times \dfrac13-10\\ =456\times 9+456\times \dfrac13-10\\ =456\times \bigg(9+\dfrac13\bigg)-10\\ =456\times \dfrac{28}3-10\\ =4256-10\\ =4246\\ 4/\\ x:13=41\\ ⇔x=41\times 13\\ ⇔x=533\\ \text{Vậy x = 533}\\ b,\ 1428:x=14\\ ⇔x=1428:14\\ ⇔x=102\\ \text{Vậy x = 102}\\ c,\ 7\times x-8=713\\ ⇔7\times x=713+8\\ ⇔7\times x=721\\⇔x=721:7\\ ⇔x=103\\ \text{Vậy x = 103}\\ d,\ (x-1954)\times 5=50\\ ⇔x-1954=50:5\\ ⇔x-1954=10\\ ⇔x=10+1954\\ ⇔x=1964\\ \text{Vậy x = 1964}\\ e,\ \left [3\times (x+2):7\right ]\times 4=120\\ ⇔3\times (x+2):7=120:4\\ ⇔3\times (x+2):7=30\\ ⇔3\times (x+2)=30\times 7\\ ⇔3\times (x+2)=210\\ ⇔x+2=210:3\\ ⇔x+2=70\\ ⇔x=70-2\\ ⇔x=68\\ \text{Vậy x = 68}\\ 6/\\ a,\ 130-x=909:9\\ ⇔130-x=101\\ ⇔x=130-101\\ ⇔x=29\\ \text{Vậy x = 29}\\ b,\ 59,8:(x-8,7)=26\\ ⇔x-8,7=59,8:26\\ ⇔x-8,7=2,3\\ ⇔x=2,3+8,7\\ ⇔x=11\\ \text{Vậy x = 11}\)

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Bài $3$.

$a$) $(42 \times 43 + 43 \times 57 + 43) - 360 : 4$

$= [43 \times (42 + 57 + 1)] - 360 : 4$

$= 43 \times 100 - 360 : 4$

$= 4300 - 90$

$= 4210$

$b$) `(372 - 19 . 4) - (981 : 9 -13)`

`= (372 - 76) - (109 - 13)`

`= 296 - 96`

`= 200`

$c$) $456 : 2 \times 18 + 456 : 3 - 10$

$= 228 \times 18 + 152 - 10$

$= 4104 + 152 - 10$

$= 4246$

Bài $4$.

$a$) $ x : 13 = 41$

$⇔ x = 41 \times 13$

$⇔ x = 533$

  Vậy $x=533$

$b$) $1428 : x = 14$

$⇔ x = 102$

  Vậy $x=102$

$c$) $7 \times x - 8 = 713$

$⇔ 7 \times x = 721$

$⇔ x = 103$

  Vậy $x=103$

$d$) $(x-1954).5=50$

$⇔ x - 1954 = 10$

$⇔ x = 1964$

  Vậy $x=1964$

$e$) $[3 \times (x+2) : 7] .4 = 120$

$⇔ 3 \times (x+2) : 7 = 30$

$⇔ (x+2) : 7 = 10$

$⇔ x + 2 = 70$

$⇔ x = 68$

  Vậy $x=68$

Bài $6$.

$a$) $130 - x = 909 : 9$

$⇔ 130 - x = 101$

$⇔ x = 29$

  Vậy $x=29$

$b$) $59,8 : (x - 8,7) = 26$

$⇔ x - 8,7 = 2,3$

$⇔ x = 11$

  Vậy $x=11$.