ai giúp em với ạ

Are there twenty - five students in your class?

 He goes to work at a quarter past fifteen.

 Are there forty classrooms in Phong's school ?

`#ava`

Gọi quãng đường lúc đi là `x(x>0)(km)`

Quãng đường lúc về là:`x+20(km)`

Thời gian đi là:`x/40`(giờ)

Thời gian đi về là : \(\dfrac{x+20}{50}\left(giờ\right)\)

Theo đề , ta có pt:

\(\dfrac{x}{40}-\dfrac{x+20}{50}=\dfrac{1}{5}\)

\(\text{⇔}\dfrac{5x-4\left(x+20\right)}{200}=\dfrac{40}{200}\)

`⇒5x−4x−80=40`

`⇔x−80=40`

`⇔x=120(km)` `(` thỏa mãn `)`

Vậy quãng đường lúc đi  `120km`

virus không phải là một cơ thể sống. Vì virus chưa có cấu tạo tế bào

\(\Leftrightarrow\left(x-3\right)\left(\dfrac{1}{13}+\dfrac{1}{14}-\dfrac{1}{15}-\dfrac{1}{16}\right)=0\)

=>x-3=0

hay x=3

`#ava`

`e)`\(\dfrac{x-3}{13}+\dfrac{x-3}{14}=\dfrac{x-3}{15}+\dfrac{x-3}{16}\)

\(\dfrac{x-3}{13}+\dfrac{x-3}{14}-\dfrac{x-3}{15}-\dfrac{x-3}{16}=0\)

\(\left(x-3\right)\left(\dfrac{1}{13}+\dfrac{1}{14}-\dfrac{1}{15}-\dfrac{1}{16}\right)=0\)

Mà : \(\dfrac{1}{13}+\dfrac{1}{14}-\dfrac{1}{15}-\dfrac{1}{16}\ne0\)

\(⇒ x − 3 = 0\)

`x=3`

Vậy `x=3`

\(\Leftrightarrow\left(x-3\right).\left(\dfrac{1}{13}+\dfrac{1}{14}\right)=\left(x-3\right)\left(\dfrac{1}{15}+\dfrac{1}{16}\right)\)

\(\Leftrightarrow\left(x-3\right)\left(\dfrac{1}{13}+\dfrac{1}{14}-\dfrac{1}{15}-\dfrac{1}{16}\right)=0\)

\(\Leftrightarrow\left(x-3\right)=0\Rightarrow x=3\)

lx

a: \(\Leftrightarrow\left(x-\dfrac{2}{3}\right)\cdot\dfrac{5}{6}=\dfrac{-4}{15}+\dfrac{2}{5}=\dfrac{-4+6}{15}=\dfrac{2}{15}\)

=>x-2/3=4/25

hay x=62/75

b: \(\Leftrightarrow x+\dfrac{1}{9}=\dfrac{2}{45}\)

=>x=2/45-1/9=2/45-5/45=-3/45=-1/15

c: \(\dfrac{17}{18}-\left(x+\dfrac{7}{12}\right)=\dfrac{1}{9}\)

=>x+7/12=17/18-1/9=17/18-2/18=15/18=5/6

=>x=5/6-7/12=10/12-7/12=1/4

d: \(\Leftrightarrow\left(x+\dfrac{13}{21}\right)\cdot\dfrac{7}{12}=\dfrac{13}{15}-\dfrac{7}{10}=\dfrac{26-21}{30}=\dfrac{1}{6}\)

=>x+13/21=1/6:7/12=1/6x12/7=12/42=2/7

=>x=2/7-13/21=-1/21