1. B

2. D

3. B

4. C

1. are - doing

2. jogs

3. is watching

4. doesn’t go

5. is skipping

\(\left|2x-6\right|-1=x\)

\(\Rightarrow\left|2x-6\right|=\pm\left(x+1\right)\)

TH1: \(x+1>0\Rightarrow x>-1\)

\(2x-6=x+1\Rightarrow2x-x=1+6\Rightarrow x=7\)

TH2: \(x+1< 0\Rightarrow x< -1\)

\(2x-6=-x-1\Rightarrow2x+x=-1+6\Rightarrow x=\dfrac{5}{3}\)

Vậy \(x\in\left\{7;\dfrac{5}{3}\right\}\).

a) \(\dfrac{1}{9}\times\dfrac{4}{7}+\dfrac{1}{9}\times\dfrac{3}{7}=\dfrac{1}{9}\times\left(\dfrac{4}{7}+\dfrac{3}{7}\right)=\dfrac{1}{9}\times1=\dfrac{1}{9}\)

b) \(\dfrac{5}{13}\times\dfrac{189}{18}-\dfrac{5}{13}\times\dfrac{9}{18}=\dfrac{5}{13}\times\left(\dfrac{189}{18}-\dfrac{9}{18}\right)=\dfrac{5}{13}\times\dfrac{180}{18}=\dfrac{5}{13}\times10=\dfrac{50}{13}\)

c) \(\dfrac{12}{7}:\dfrac{4}{9}+\dfrac{4}{7}:\dfrac{4}{9}=\dfrac{12}{7}\times\dfrac{9}{4}+\dfrac{4}{7}\times\dfrac{9}{4}=\left(\dfrac{12}{7}+\dfrac{4}{7}\right)\times\dfrac{9}{4}=\dfrac{16}{7}\times\dfrac{9}{4}=\dfrac{144}{28}=\dfrac{36}{7}\)

Chọn phương án C.

Trang trại đó còn số con gà là:

\(28415-12154-9475=6768\) (con gà)

Đ/s: 6768 con gà

Chọn phương án B.