=0,25 x X +0,75 x X +X x1=35

=X x (0,25 +0,75 +1)=35

=X x 2=35

 X = 35:2

 X = 17,5

chưa học tha cho em

Bài 1: 

Ta có: \(x-35\%\cdot x=\dfrac{1}{25}\)

\(\Leftrightarrow65\%\cdot x=\dfrac{1}{25}\)

\(\Leftrightarrow x=\dfrac{1}{25}:\dfrac{13}{20}=\dfrac{1}{25}\cdot\dfrac{20}{13}=\dfrac{4}{65}\)

Vậy: \(x=\dfrac{4}{65}\)

Bài 2: 

a) Ta có: \(17\dfrac{2}{31}-\left(\dfrac{15}{17}+6\dfrac{2}{31}\right)\)

\(=17\dfrac{2}{31}-\dfrac{15}{17}-6\dfrac{2}{31}\)

\(=11+\dfrac{2}{31}-\dfrac{15}{17}\)

\(=\dfrac{5366}{527}\)

=> cái vế  trong ngoặc là 0.

rồi bạn làm tiếp nha

\(\dfrac{-12}{25}.\left(\dfrac{3}{4}-x+\dfrac{6}{-11}-\dfrac{5}{6}\right)=0\)

\(\dfrac{3}{4}-x+\dfrac{-6}{11}-\dfrac{5}{6}=0\)

\(\dfrac{3}{4}-x+\dfrac{-91}{66}=0\)

\(\dfrac{3}{4}-x=0-\left(\dfrac{-91}{66}\right)\)

\(\dfrac{3}{4}-x=\dfrac{91}{66}\)

\(x=\dfrac{-83}{132}\)

a: \(\overline{xx}+\overline{x}+5=125\)

=>10x+x+x=120

=>12x=120

=>x=10

b: \(\overline{xxx}+\overline{xx}+x+x=992\)

=>100x+10x+x+10x+x+2x=992

=>124x=992

=>x=8(nhận)

c: \(4725+\overline{xxx}+\overline{xx}+\overline{x}=54909\)

=>100x+10x+x+10x+x+x=54909-4725

=>123x=50184

=>x=408

d: \(\overline{xxx}-\overline{xx}-\overline{x}-25=4430\)

=>100x+10x+x-10x-x-x=4430+25

=>99x=4425

=>x=4425/99(loại)

e: \(\overline{xxx}+\overline{xx}+\overline{x}+\overline{x}+\overline{x}+1=1001\)

=>111x+11x+3x=1000

=>125x=1000

=>x=8

f: \(35655-\overline{xxx}-\overline{xx}-\overline{x}=5274\)

=>35655-111x-11x-x=5274

=>35655-123x=5274

=>123x=35655-5274=30381

=>x=247

8125

8125

C. % A = 35%; % T =35% ; %G = 15%; X = 15%

a

\(xxx-xx-x-25=443\)\(0\)

\(xxx-xx-x=4430-\)\(25\)

\(xxx-xx-x=4405\)

\(x=4405:5\)

\(x=881\)

\(Thử\)\(lại\)\(:\)

\(881.881.881\)\(-881.881\)\(-881-25\)

\(=683797841\)\(-776161\)\(-881-25\)

\(=683021680-881\)\(-25\)

\(Mình\)\(nhầm\)\(cho\)\(xin\)\(lỗi\)\(nhé\)