X * (12,35 + 12,65) = 875

X * 25 = 875

X = 875 : 25

X = 35

x*(12,35+12,65)=875

x*25=875

x=35

a) X*(12,35+12,65)=875

X*25=875

X=875:25

X=35

b) X+X*2,7+X*6,3=120

X*(1+2,7+6,3)=120

X*10=120

X=120:10

X=12

a) X*(12,35+12,65)=875

X*25=875

X=875:25

X=35

b) X+X*2,7+X*6,3=120

X*(1+2,7+6,3)=120

X*10=120

X=120:10

X=12

x.(12,25+12,65)=875

x.25=875

x=875:25

x=35

\(x\times12,35+x\times12,65=875\)

=>X x (12,35+12,65)=875

=>X x 25                =875

=>X                        = 875:25=35

\(x+x\times2,7+x\times6,3=120\)

câu này tương tự như trên bạn nhé!

x.12.35+x.12,65=875

x.(12,35+12,65)=875

x. 25=875

x=875: 25

x=35

x nhân 12,35+x nhân 12,56=875

x nhân (12,35+12,65)         =875

x nhân 25                          =875

x                                       =875 :25

x                                       =35

x . 12,35 + x . 12,65 = 875

x . ( 12,35 + 12,65 ) = 875

x . 25 = 875

x = 875 : 25

x = 35

x . 12,35 + x . 12,65 = 875

x. ( 12,35 + 12,65 ) = 875

x . 25 =875

x = 875 : 25

x= 35

phần b tự làm

\(\frac{x}{2}=\frac{y}{3}\Rightarrow\frac{x}{8}=\frac{y}{12}\) (1)

\(\frac{y}{4}=\frac{z}{5}\Rightarrow\frac{y}{12}=\frac{z}{15}\)(2)

Từ (1) và (2) \(\Rightarrow\frac{x}{8}=\frac{y}{12}=\frac{z}{15}\)

Đặt : \(\frac{x}{8}=\frac{y}{12}=\frac{z}{15}=k\) \(\Rightarrow x=8k\); \(y=12k\) ; \(z=15k\)

\(x+y+z=875\Rightarrow8k+12k+15k=875\Rightarrow35k=875\Rightarrow k=25\)

Do đó : 

\(\frac{x}{8}=25\Rightarrow x=25.8=200\)

\(\frac{y}{12}=25\Rightarrow y=25.12=300\)

\(\frac{z}{15}=25\Rightarrow z=25.15=375\)

Vậy ......

Ta có:

\(\frac{x}{2}=\frac{y}{3};\frac{y}{4}=\frac{z}{5}\Leftrightarrow\frac{x}{8}=\frac{y}{12}=\frac{z}{15}\) và \(x+y+z=875\)

Áp dụng tính chất của dãy tỉ số bằng nhau:

\(\frac{x}{8}=\frac{y}{12}=\frac{z}{15}=\frac{x+y+z}{8+12+15}=\frac{875}{35}=25\)

\(\hept{\begin{cases}\frac{x}{8}=25\Rightarrow x=25.8=200\\\frac{y}{12}=25\Rightarrow y=25.12=300\\\frac{z}{15}=25\Rightarrow z=25.15=375\end{cases}}\)

Vậy x = 200; y = 300; z = 375

a) \(980+y:94=8245\)

\(y:94=7265\)

\(y=7265\times94\)

\(y=682910\)

b) \(45\times y\times36=3240\)

\(45\times y=3240:36\)

\(45\times y=90\)

\(y=90:45\)

\(y=2\)

c) \(3865-y+875=1000\)

\(3865-y=125\)

\(y=3865-125\)

\(y=3740\)

d) \(4788:126\times y=1596\)

\(126\times y=4788:1596\)

\(126\times y=3\)

\(y=\dfrac{3}{126}\)

\(y=\dfrac{1}{42}\)

e) \(24624:y:9=76\)

\(y:9=24624:76\)

\(y:9=324\)

\(y=324\times9\)

\(y=2916\)

\(x.\left(12,35+12,65\right)=875\\ x=\dfrac{875}{25}=35\)

Đặt \(\frac{x}{5}=\frac{y}{7}=k\Rightarrow x=5k;y=7k\)

Thay \(x=5k;y=7k\) ta có:

\(5k\times7k=875\)

\(\Leftrightarrow k^2=875\div\left(5\times7\right)\)

\(\Leftrightarrow k^2=25\)

\(\Rightarrow k=\pm5\)

TH1: \(k=5\)

\(\Rightarrow\hept{\begin{cases}x=5\times5=25\\y=7\times5=35\end{cases}}\)

TH2: \(k=-5\)

\(\Rightarrow\hept{\begin{cases}x=5\times\left(-5\right)=-25\\y=7\times\left(-5\right)=-35\end{cases}}\)

Vậy ...

Đặt :

\(\frac{x}{5}=\frac{y}{7}=k\) \(\Leftrightarrow\hept{\begin{cases}x=5k\\y=7k\end{cases}}\)

Mà \(xy=875\)

\(\Leftrightarrow5k.7k=875\)

\(\Leftrightarrow35k^2=875\)

\(k^2=25\)

\(\Leftrightarrow\orbr{\begin{cases}k=5\\k=-5\end{cases}}\)

+) Với \(k=5\Leftrightarrow\hept{\begin{cases}x=25\\y=35\end{cases}}\)

+) Với \(k=-5\Leftrightarrow\orbr{\begin{cases}x=-25\\y=-35\end{cases}}\)

Ta có: \(x.y=875\Rightarrow x=875:y_{\left(1\right)}\)

Thay (1) vào \(\frac{x}{5}=\frac{y}{7}\), ta được:

\(\frac{875:y}{5}=\frac{y}{7}\Rightarrow\frac{175}{y}=\frac{y}{7}\)

\(\Leftrightarrow175.7=y.y\)

\(\Leftrightarrow1225=y^2\)

\(\Leftrightarrow y=\pm35\)

\(y=35\Rightarrow x=875:y=875:35=25\)

\(y=-35\Rightarrow x=875:\left(-35\right)=-25\)

Vậy \(y=35;x=25\)

       \(y=-35;x=-25\)

Tớ nek, hi bn