\(x+15,7=7,2\times2,5\)
    \(x+15,7=18\) 
    \(x=18-15,7\)   
    \(x=2,3\)
    Vậy \(x=2,3\)


    \(x\times9,1+x\times1,9=26,4\)
⇔\(x\times\left(9,1+1,9\right)=26,4\)
    \(x\times10=26,4\)
    \(x=26,4:10\)
    \(x=2,64\)
    Vậy \(x=2,64\)


    \(x:12,5=48-45,66\)
    \(x:12,5=2,34\)
    \(x=2,34\times12,5\)
    \(x=29,25\)
    Vậy \(x=29,25\)


    Sửa đề:
    \(x\times9,9+x\times10=12,5\)
⇔\(x\times\left(9,9+10\right)=12,5\)
    \(x\times19,9=12,5\)
    \(x=12,5:19,9\)
    \(x=\dfrac{125}{199}\)
    Vậy \(x=\dfrac{125}{199}\)
\(#PeaGea\)

xxxx

\(x\cdot9,9+x:10=12,5\)

\(x\cdot9,9+x\cdot\frac{1}{10}=12,5\)

\(x\cdot\left(9,9+\frac{1}{10}\right)=12,5\)

\(x\cdot\left(\frac{99}{10}+\frac{1}{10}\right)=12,5\)

\(x\cdot\frac{100}{10}=12,5\)

\(x\cdot10=12,5\)

\(x=12,5:10\)

\(x=1,25\)

   Vậy x = 1,25

X.99+X:10=12,5

X.99+X*1/10=12,5

X.(99+1/10)=12,5

X.99,1=12,5

X=12,5/99=125/991

X.99+X:10=12,5

X.99+X.0,1=12,5

X.(99+0,1)=12,5

X.99,1=12,5

X=12,5:99,1

X=0,126135217

a, x . 9,9 + x : 10 = 12,5

\(x.\frac{99}{10}+x.\frac{1}{10}=\frac{25}{2}\)

\(x\left(\frac{99}{10}+\frac{1}{10}\right)=\frac{25}{2}\)

\(x.10=\frac{25}{2}\)

\(x=\frac{25}{2}:10=\frac{25}{2}.\frac{1}{10}=\frac{5}{4}\)

b, \(x:\frac{1}{4}-x=\frac{78}{5}\)

\(x.4-x=\frac{78}{5}\)

\(x\left(4-1\right)=\frac{78}{5}\)

\(x.3=\frac{78}{5}\)

\(x=\frac{78}{5}:3=\frac{78}{5}.\frac{1}{3}=\frac{26}{5}\)

c, \(x:\frac{1}{10}-x:4-x.\frac{3}{4}=\frac{9}{4}\)

\(=x.10-x.\frac{1}{4}-x.\frac{3}{4}=\frac{9}{4}\)

\(x\left(10-\frac{1}{4}-\frac{3}{4}\right)=\frac{9}{4}\)

\(x.9=\frac{9}{4}\)

\(x=\frac{9}{4}:9=\frac{9}{4}.\frac{1}{9}=\frac{1}{4}\)

**** 

Thừa số thứ nhất (0x1,1x2,2x3,3x.......x9,9) bằng 0 (vì số nào nhân với 0 cũng bằng 0).

Do đó kết quả của bài toán là 0 ( 0 x (1+2+3+........+ 99 + 100) = 0)

Vì (0x1,1x2,2x3,3x...x9,9)=0 

=>(0x1,1x2,2x3,3x...x9,9)x(1+2+3+...+99+100)=0x(1+2+3+...+99+100)=0

\(a,x+3,79=15,12\)\(\Rightarrow x=15,12-3,79\)\(\Rightarrow x=11,33\)

\(b,12,1-x=5,49\)\(\Rightarrow x=12,1-5,49\Rightarrow x=6,61\)

\(c,60,45:x=1,5\)\(\Rightarrow x=60,45:1,5\Rightarrow x=40,3\)

\(d,3,5.x-1,5.x=12,5\)

\(\Rightarrow x\left(3,5-1,5\right)=12,5\)

\(\Rightarrow x.2=12,25\Rightarrow x=12,25:2=6,125\)

\(d,12,5.x-2,5.x-50=2,5.10\)

\(\Rightarrow12,5.x-2,5.x-50=25\)

\(\Rightarrow x\left(12,5-2,5\right)=25+50\)

\(\Rightarrow x.10=75\)

\(\Rightarrow x=75:10=7,5\)

a) x=11,33                  b) x=6,61                  c)40,3

     Mình chỉ biết làm tới đó thôi. xin lỗi nha

x*2+x.4=12.5

x*6=12.5

x=12.5/6

x=6.25

\(x:\frac{1}{2}+x.4-x=12,5\Rightarrow x.2+x.4-x=12,5\Rightarrow x.\left(2+4-1\right)=12,5\Rightarrow x.5=12,5\Rightarrow x=12,5:5=2,5\)

`=>` Ta có `x` là:

0,15 : 12,5/100 = 1,2` (tấn)

\(x=0,15:12,5\times100=1,2\) (tấn)