\(#NgNgoc0409\)

Gọi số chai sữa tắm là : \(x\left(x\in Z+\right)\)

\(=>\) số chai dầu gội là: \(45-x\)

Theo bài ra, ta có: 

\(50000.\left(45-x\right)+60000x+600000=3000000\)

\(=>2250000-50000x+60000x=2400000\)

\(\left(=\right)2250000+10000x=2400000\)

\(\left(=\right)10000x=150000\)

\(\left(=\right)x=15\)

Vậy anh Minh mua 15 chai sữa tắm.

\(#NgNgoc0409\)

\(x\notin\left\{-3;3\right\}\)

\(A=\dfrac{2x}{x+3}+\dfrac{x+1}{x-3}+\dfrac{3-11x}{9-x^2}\)

\(=\dfrac{2x\left(x-3\right)}{\left(x+3\right)\left(x-3\right)}+\dfrac{\left(x+1\right)\left(x+3\right)}{\left(x-3\right)\left(x+3\right)}+\dfrac{11x-3}{x^2-9}\)

\(=\dfrac{2x^2-6x}{x^2-9}+\dfrac{x^2+4x+3}{x^2-9}+\dfrac{11x-3}{x^2-9}\)

\(=\dfrac{3x^2+9x}{x^2-9}\)

\(=\dfrac{3x\left(x+3\right)}{\left(x-3\right)\left(x+3\right)}\)

\(=\dfrac{3x}{x-3}\)

\(#NgNgoc0409\)

Ta có: \(\dfrac{5z-3y}{4}=\dfrac{3x-4z}{5}=\dfrac{4y-5z}{3}\)

\(=>\dfrac{20z-12y}{16}=\dfrac{15x-20z}{25}=\dfrac{12y-15x}{9}\)

Áp dụng tính chất dãy tỉ số bằng nhau, ta có: 

\(\dfrac{20z-12y}{16}=\dfrac{15x-20z}{25}=\dfrac{12y-15x}{9}=\dfrac{20z-12y+15x-20z+12y-15x}{16+25+9}=0\)

\(=>\left\{{}\begin{matrix}\dfrac{20z-12y}{16}=0\\\dfrac{15x-20z}{25}=0\end{matrix}\right.\)       \(\left(=\right)\left\{{}\begin{matrix}20z-12y=0\\15x-20z=0\end{matrix}\right.\)    \(\left(=\right)\left\{{}\begin{matrix}20z=12y\\15x=20z\end{matrix}\right.\)   \(\left(=\right)\left\{{}\begin{matrix}\dfrac{z}{3}=\dfrac{y}{5}\\\dfrac{x}{4}=\dfrac{z}{3}\end{matrix}\right.\)

\(=>\dfrac{x}{4}=\dfrac{y}{5}=\dfrac{z}{3}\)

\(=>x:y:z=4:5:3\left(dpcm\right)\)

\(\dfrac{3}{11}\)

Em kbt cách lp 5 là cách nào:(((

Gọi chiều dài là: \(a\) chiều rộng là: \(b\)          \(\left(a,b>0\right)\)

Ta có: \(120\%a\times80\%b=a\times b-160\)

\(\Rightarrow\dfrac{6}{5}a\times\dfrac{4}{5}b=a\times b-160\)

\(\Leftrightarrow\dfrac{24}{25}\times a\times b=a\times b-160\)

\(\Leftrightarrow a\times b-\dfrac{24}{25}\times a\times b=160\)

\(\Leftrightarrow\dfrac{1}{25}\times a\times b=160\)

\(\Leftrightarrow a\times b=4000\)

Vậy diện tích hình chữ nhật ban đầu là: \(4000cm^2\)

Ta có: \(3x+5y⋮7\)

\(=>3x+5y+7y⋮7\)

\(\Leftrightarrow3\left(x+4y\right)⋮7\)

Vì \(3⋮̸\)\(7\) nên \(x+4y⋮7\)     (đpcm)