a) x - 7 = 5. 0 => x - 7 = 0 =>x = 7.

b) x: 3 = 47 +13 => x: 3 = 60 => x = 60.3 => x = 180.

c) x :  7 - 7 = 0 hoặc x : 12 - 12 = 0. Do đó x = 49 hoặc x = 144.

d) x : 2 = 150 - 135 => x: 2 = 15 => x = 15.2 => x = 30.

e) 100: x = 140 -120 => 100: x = 20 => x = 100:20 => x = 5.

g) x : 5 = 300 - 273 => x : 5 = 27 =>x = 27.5 => x = 135

a) x - 7 = 5. 0 => x - 7 = 0 =>x = 7.

b) x: 3 = 47 +13 => x: 3 = 60 => x = 60.3 => x = 180.

c) x :  7 - 7 = 0 hoặc x : 12 - 12 = 0. Do đó x = 49 hoặc x = 144.

d) x : 2 = 150 - 135 => x: 2 = 15 => x = 15.2 => x = 30.

e) 100: x = 140 -120 => 100: x = 20 => x = 100:20 => x = 5.

g) x : 5 = 300 - 273 => x : 5 = 27 =>x = 27.5 => x = 135

           Bài làm :

\(a\text{)}...\Leftrightarrow\orbr{\begin{cases}x\div7-7=0\\x.3-12=0\end{cases}}\Leftrightarrow\orbr{\begin{cases}x\div7=7\\x.3=12\end{cases}}\Leftrightarrow\orbr{\begin{cases}x=49\\x=4\end{cases}}\)

\(b\text{)}\Leftrightarrow...\Leftrightarrow x\div2=15\Leftrightarrow x=15.2=30\)

\(c\text{)}...\Leftrightarrow100\div x=20\Leftrightarrow x=100\div20=5\)

\(d\text{)}...\Leftrightarrow x\div5=27\Leftrightarrow x=27.5=135\)

Sửa đề; \(\dfrac{x-342}{15}+\dfrac{x-323}{17}+\dfrac{x-300}{19}+\dfrac{x-273}{21}=10\)

\(\Leftrightarrow x-357=0\)

hay x=357

\(a,\left(x-7\right):5=0\)

\(\Rightarrow x-7=0\)

\(\Rightarrow x=7\)

\(b,\left(x:7-7\right)\left(x:12-12\right)=0\)

\(\Rightarrow\hept{\begin{cases}x:7=7\\x:12=12\end{cases}}\)

\(\Rightarrow x=1\)

\(c,300-x:5=273\)

\(\Rightarrow x:5=27\)

\(\Rightarrow x=27.5=135\)

\(d,135+x:2=150\)

\(\Rightarrow x:2=15\)

\(\Rightarrow x=30\)

a) \(\left(x-7\right):5=0\)

\(\Rightarrow x-7=0\times5\)

\(\Rightarrow x-7=0\)

\(\Rightarrow x=0+7\)

\(\Rightarrow x=7\)

Vậy x = 7

b) \(\left(x:7-7\right)\left(x:12-12\right)=0\)

\(\Rightarrow\orbr{\begin{cases}x:7-7=0\\x:12-12=0\end{cases}}\Rightarrow\orbr{\begin{cases}x:7=7\\x:12=12\end{cases}}\Rightarrow\orbr{\begin{cases}x=49\\x=144\end{cases}}\)

Vậy x = 49 hoặc x = 144

c) \(300-x:5=273\)

\(\Rightarrow x:5=300-273\)

\(\Rightarrow x:5=27\)

\(\Rightarrow x=27\times5\)

\(\Rightarrow x=135\)

Vậy x = 135

d) \(135+x:2=150\)

\(\Rightarrow x:2=150-135\)

\(\Rightarrow x:2=15\)

\(\Rightarrow x=15\times2\)

\(\Rightarrow x=30\)

Vậy x = 30

_Chúc bạn học tốt_

x : 60 = 273

x = 273×60

x = 16380

Vậy x = 16380.

Đáp án A

Lời giải:
PT $\Leftrightarrow \frac{x-342}{15}-1+\frac{x-323}{17}-2+\frac{x-300}{19}-3+\frac{x-273}{21}-4=0$

$\Leftrightarrow \frac{x-357}{15}+\frac{x-357}{17}+\frac{x-357}{19}+\frac{x-357}{21}=0$

$(x-357)\left(\frac{1}{15}+\frac{1}{17}+\frac{1}{19}+\frac{1}{21}\right)=0$

Dễ thấy: $\frac{1}{15}+\frac{1}{17}+\frac{1}{19}+\frac{1}{21}\neq 0$

$\Rightarrow x-357=0$

$\Rightarrow x=357$