\(\dfrac{2}{7}x\dfrac{4}{5}-\dfrac{2}{7}x\dfrac{1}{3}\)
\(\dfrac{2}{7}x\left(\dfrac{4}{5}-\dfrac{2}{7}\right)\)
\(\dfrac{2}{7}x.\left(\dfrac{28}{35}-\dfrac{10}{35}\right)\)
\(\dfrac{2}{7}x.\dfrac{18}{35}\)
Hình như bn ghi thiếu đề bài?

III.
1A
2A
IV
1C
2D
3B
4D
5B
6C
7D
8B
9D
10D

\(x\in\infty\)

\(147-7\cdot\left(x+3\right)=98\)
\(7\left(x+3\right)=147-98\)
\(7\left(x+3\right)=49\)
\(x+3=49:7\)
\(x+3=7\)
\(x=7-3\)
\(x=4\)
Vậy \(x=4\)

\(15+25+35+...+85+95\)
\(=95+\left(85+15\right)+\left(75+25\right)+\left(65+35\right)+\left(55+45\right)\)
\(=95+100+100+100+100\)
\(=100.4+95\)
\(=400+95\)
\(=495\)

\(\dfrac{3}{2}x+\dfrac{3}{4}=\dfrac{4}{5}-x\)
\(\dfrac{3}{2}x+x=\dfrac{4}{5}-\dfrac{3}{4}\)
\(x\left(\dfrac{3}{2}+1\right)=\dfrac{16}{20}-\dfrac{15}{20}\)
\(x\left(\dfrac{3}{2}+\dfrac{2}{2}\right)=\dfrac{1}{20}\)
\(x.\dfrac{5}{2}=\dfrac{1}{20}\)
\(x=\dfrac{1}{20}:\dfrac{5}{2}\)
\(x=\dfrac{1}{20}.\dfrac{2}{5}\)
\(x=\dfrac{1.1}{10.5}\)
\(x=\dfrac{1}{50}\)
Vậy ....

\(\left(2x-1\right)+\dfrac{1}{4}=75\%\)
\(\left(2x-1\right)+\dfrac{1}{4}=\dfrac{3}{4}\)
\(2x-1=\dfrac{3}{4}-\dfrac{1}{4}\)
\(2x-1=\dfrac{2}{4}\)
\(2x-1=\dfrac{1}{2}\)
\(2x=\dfrac{1}{2}+1\)
\(2x=\dfrac{1}{2}+\dfrac{2}{2}\)
\(2x=\dfrac{3}{2}\)
\(x=\dfrac{3}{2}:2\)
\(x=\dfrac{3}{2}.\dfrac{1}{2}\)
\(x=\dfrac{3}{4}\)
Vậy...

\(2.x-3=5\)
\(2x=5+3\)
\(2x=8\)
\(x=8:2\)
\(x=4\)
Vậy....

\(a,\dfrac{3}{a}-\dfrac{4}{7}=1-\dfrac{34}{35}\)
\(\dfrac{3}{a}-\dfrac{4}{7}=\dfrac{35}{35}-\dfrac{34}{35}\)
\(\dfrac{3}{a}-\dfrac{4}{7}=\dfrac{1}{35}\)
\(\dfrac{3}{a}=\dfrac{1}{35}+\dfrac{4}{7}\)
\(\dfrac{3}{a}=\dfrac{1}{35}+\dfrac{20}{35}\)
\(\dfrac{3}{a}=\dfrac{21}{35}\)
\(\dfrac{3}{a}=\dfrac{3}{5}\)
\(a=5\)
Vậy....
\(b,\dfrac{5+a}{12}=\dfrac{2}{3}\)
\(\left(5+a\right).3=2.12\)
\(\left(5+a\right).3=24\)
\(5+a=24:3\)
\(5+a=8\)
\(x=8-5\)
\(x=3\)
Vậy...

Cô ơi, lại có bão mới ạ?:(( Hễ mà còn bão thì chúc các bạn ở vùng bão hoặc chịu ảnh hưởng của bão luôn luôn an toàn ạ :((