x+10%=y
y+10%=13,31
[tex]y+ \frac{10}{100} *y=13,31[/tex]
[tex]y* (\frac{1}{10} +1)[/tex]=13,31
[tex]y* \frac{11}{10} =13,31[/tex]
[tex]y=13,31* \frac{10}{11} \\ y=12,1[/tex]
[tex]x+ \frac{10}{100} *x=12,1 \\ x*(1+ \frac{1}{10} )=12,1 \\ x* \frac{11}{10}=12,1 \\ x=12,1* \frac{10}{11} \\ x=11[/tex]
Prețul inițial este 11 lei
