`x + 4/5= 45/5 -( 3/7 + 3/5)`

`=> x+ 4/5=9 - 36/35`

`=> x+ 4/5=279/35`

`=> x= 279/35 -4/5`

`=>x= 251/35`

__

`5/7 + x/35 = 4/5`

`=>  x/35 = 4/5-5/7`

`=>  x/35 =28/35 - 25/35`

`=> x/35= 3/35`

`=>x=3`

`@ `\(MinYewCou\)

ok

\(a,x+\dfrac{4}{5}=\dfrac{45}{5}-\left(\dfrac{3}{7}+\dfrac{3}{5}\right)\)

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

\(x+\dfrac{4}{9}=\dfrac{279}{35}\)

\(x=\dfrac{279}{35}-\dfrac{4}{9}\)

\(x=\dfrac{251}{35}\)

\(b,\dfrac{5}{7}+\dfrac{x}{35}=\dfrac{4}{5}\)

\(\dfrac{5}{7}+\dfrac{x}{35}-\dfrac{4}{5}=0\)

\(\dfrac{25}{35}+\dfrac{x}{35}-\dfrac{28}{35}=0\)

\(25+x-28=0\)

\(x=3\)

hazz

a/ \(\frac{28-x}{35}=\frac{5}{7}\Rightarrow7\left(28-x\right)=35.5\Rightarrow196-7x=175\Rightarrow7x=21\Rightarrow x=3\)

b/ \(\frac{x+11}{35}=\frac{4}{5}\Rightarrow5\left(x+11\right)=35.4\Rightarrow5x+55=140\Rightarrow5x=85\Rightarrow x=17\)

\(x+\frac{4}{5}=\frac{45}{5}-\left(\frac{3}{7}+\frac{3}{5}\right)\)

\(x+\frac{4}{5}=9-\frac{36}{35}\)

\(x+\frac{4}{5}=\frac{279}{35}\)

\(\Rightarrow x=\frac{251}{35}\)

\(x+\frac{4}{5}=\frac{45}{5}-\left(\frac{3}{7}+\frac{3}{5}\right)\)

\(\Leftrightarrow x+\frac{4}{5}=9-\left(\frac{3}{7}+\frac{3}{5}\right)\)

\(\Leftrightarrow x+\frac{4}{5}=9-\frac{3}{7}-\frac{3}{5}\)

\(\Leftrightarrow x+\frac{4}{5}=\frac{315}{35}-\frac{15}{35}-\frac{21}{35}\)

\(\Leftrightarrow x+\frac{4}{5}=\frac{279}{35}\)

\(\Leftrightarrow x=\frac{279}{35}-\frac{4}{5}\)

\(\Leftrightarrow x=\frac{251}{35}\)

\(\frac{5}{7}+\frac{x}{35}=\frac{4}{5}\)

\(\Leftrightarrow\frac{25}{35}+\frac{x}{35}=\frac{28}{35}\)

\(\Leftrightarrow25+x=28\)

\(\Leftrightarrow x=28-25\)

\(\Leftrightarrow x=3\)

a, ta thấy cả hai vế đều có 4/5 mà lại bằng nhau nên x bằng số hạng còn lại ở vế phải 

x=3/7+3/5

x=36/35

b,x là số hạng chưa biết nên

x=4/5-5/7

x=3/35

cảm ơn Kiều Ngọc Lan tớ đứng đầu olm lớp 4 đấy

cái gì đấy lỗi à

lỗi

Lỗi rồi nha! -_-

`x+4/5=4/5+(3/7+3/5)`

`=> x+4/5=4/5+36/35`

`=> x+4/5= 64/35`

`=>x= 64/35 -4/5`

`=>x=  64/35 - 28/35`

`=>x= 36/35`

`----`

`5/7 + x/35 =4/5`

`=>x/35 =4/5-5/7`

`=>x/35 =28/35 - 25/35`

`=> x/35= 3/35`

`=>x=3`

Học sinh nhẩm và ghi kết quả như sau:

7 x 5 = 35

7 x 6 = 42

7 x 2 = 14

7 x 4 = 28

35 : 7 =5

42 : 7 = 6

14 : 7 = 2

28: 7 =4

35 : 5 = 7

42 : 6 = 7

14 : 2 = 7

28 : 4 = 7