Ngày thứ 3 bán được số % gạo so với cả 3 ngày là:
100%-35%-40%=25%

Vậy ngày thứ 3 bán được số kg gạo là;

\(7200\times25\%=1800\left(kg\right)\)

\(\dfrac{5}{11}+\dfrac{4}{11}=1\)

\(\dfrac{11}{10}+\dfrac{9}{10}=\dfrac{20}{10}=2\)

\(\dfrac{11}{12}+\dfrac{5}{12}=\dfrac{16}{12}=\dfrac{4}{3}\)

\(\dfrac{7}{9}+\dfrac{5}{9}=\dfrac{12}{9}=\dfrac{4}{3}\)

0,0023

\(a,S=1-5+5^2-5^3+...+5^{98}-5^{99}\\ 5S=5-5^2+5^3-5^4+...+5^{99}-5^{100}\\ 5S+S=1-5^{100}\\ S=\dfrac{1-5^{100}}{6}\)

\(Do\) \(S\in Z\Rightarrow1-5^{100}⋮6\Rightarrow5^{100}\) chia 6 dư 1

\(a,\left(x-5\right)\left(2x-1\right)=0\\ \Rightarrow\left\{{}\begin{matrix}x-5=0\\2x-1=0\end{matrix}\right.\Rightarrow\left\{{}\begin{matrix}x=5\\x=\dfrac{1}{2}\end{matrix}\right.\)

\(b,\dfrac{2x+3}{2}-\dfrac{x+1}{3}=\dfrac{x+8}{6}\)

\(\Rightarrow\)\(\dfrac{6x+9}{6}-\dfrac{2x+2}{6}=\dfrac{x+8}{6}\)

\(\Rightarrow\)\(\dfrac{4x-7}{6}=\dfrac{x+8}{6}\Rightarrow4x-7=x+8\)

\(\Rightarrow3x=15\Rightarrow x=5\)

\(c,\dfrac{x-1}{x}+\dfrac{1}{x+1}=\dfrac{2x-1}{x^2+x}\)

\(\Rightarrow\)\(\dfrac{\left(x-1\right).\left(x+1\right)}{x\left(x+1\right)}+\dfrac{x}{x\left(x+1\right)}=\dfrac{2x-1}{x^2+x}\)

\(\Rightarrow\)\(\dfrac{x^2-1+x}{x^2+x}=\dfrac{2x-1}{x^2+x}\)

\(\Rightarrow x^2+x-1=2x-1\)

\(\Rightarrow x^2=x\Rightarrow x=0;1\)

\(\dfrac{a}{b}=\dfrac{a\left(b+c\right)}{b\left(b+c\right)}=\dfrac{ab+ac}{b^2+bc}\)

\(\dfrac{a+c}{b+c}=\dfrac{b\left(a+c\right)}{b\left(b+c\right)}=\dfrac{ba+bc}{b^2+bc}\)

Do \(ab=ba;ac< bc\) do \(\dfrac{a}{b}< 1\) hay \(a< b\)

\(\Rightarrow ab+ac< bc+ba\)

\(Vậy\) \(\dfrac{a}{b}< \dfrac{a+c}{b+c}\) \(\left(đpcm\right)\)