\(A=\dfrac{6n+5}{n+2}=\dfrac{6\left(n+2\right)-7}{n+2}=6-\dfrac{7}{n+2}\)

\(A\in Z\Leftrightarrow\dfrac{7}{n+2}\in Z\Rightarrow n+2=Ư\left(7\right)\)

\(\Rightarrow n+2=\left\{-7;-1;1;7\right\}\)

\(\Rightarrow n=\left\{-9;-3;-1;5\right\}\)

DIện tích xung quanh của căn phòng là : \(\left(8+5\right)\times2\times3.5=91m^2\)

Diện tích trần nhà là : \(8\times5=40m^2\)

Diện tích cần quét sơn là : \(91+40-8,5=122.5m^2\)

Số tiền cần quét vôi là : \(122.5\times26000=3\text{ }185\text{ }000\text{ đồng}\)

   12,87 - 14,7 + 14,13 - 37,3

= -2,17 + 14,13 - 37,3

= 11,04 - 37,3

= -26,26

`Answer:`

\(B=\frac{2021}{1}+\frac{2020}{2}+\frac{2019}{3}+...+\frac{1}{2021}\)

\(=\left(1+1+...+1\right)+\frac{2020}{2}+\frac{2019}{3}+...+\frac{1}{2021}\)

\(=\left(1+\frac{2020}{2}\right)+\left(1+\frac{2019}{3}\right)+...+\left(\frac{1}{2021}+1\right)+1\)

\(=\frac{2022}{2}+\frac{2022}{3}+...+\frac{2022}{2021}+\frac{2022}{2022}\)

\(=2022.\left(\frac{1}{2}+\frac{1}{3}+...+\frac{1}{2021}+\frac{1}{2022}\right)\)

\(\Rightarrow\frac{B}{A}=\frac{2022.\left(\frac{1}{2}+\frac{1}{3}+...+\frac{1}{2021}+\frac{1}{2022}\right)}{\frac{1}{2}+\frac{1}{3}+\frac{1}{4}+...+\frac{1}{2022}}=\frac{2022}{1}\)

ta có 

\(B=2021+\frac{2020}{2}+\frac{2019}{3}+..+\frac{1}{2021}=\left(\frac{2020}{2}+1\right)+\left(\frac{2019}{3}+1\right)+..+\left(\frac{1}{2021}+1\right)+1\)

\(=\frac{2022}{2}+\frac{2022}{3}+..+\frac{2022}{2021}+\frac{2022}{2022}=2022\left(\frac{1}{2}+\frac{1}{3}+..+\frac{1}{2022}\right)=2022\times A\)

Do đó tỉ số B/A = 2022

A=\(\dfrac{1}{2}\)+\(\dfrac{1}{3}\)+\(\dfrac{1}{4}\)+...+\(\dfrac{1}{2021}\)