[tex]x\to pretul \ initial \\\\ 10\% \ din \ x \to \frac{\not10}{\not100}*x = \frac{1}{10}*x \to \frac{x}{10} - prima \ scadere \\\\ x^{(10}-\frac{x}{10}=\frac{10x-x}{10} \to \frac{9x}{10}-noul \ pret \\\\ 10\% \ din \ \frac{9x}{10} = \frac{\not10}{\not100}* \frac{9x}{10}=\frac{1}{10}*\frac{9x}{10}\to \frac{9x}{100}-a \ doua \ scadere \\\\ \frac{9x}{10}^{(10}-\frac{9x}{100}=\frac{90x-9x}{100}\to \frac{81x}{100}-noul \ nou \ pret \\\\\\ \frac{81x}{100}=810 \\\\ x=\frac{\not810*100}{\not81} \\\\ x=10*100 [/tex]
[tex]\boxed{x=1000\ lei} \\\\ b) p\% \ din \ 1000=810 \\\\ \frac{p}{\not100}*\not1000=810 \\\\ p*10=810 \\\\ p=\frac{\not810}{\not10} \\\\\ p=81\%\\\\100\% -81\% \Longrightarrow \boxed{19\%-procentul \ dupa \ cele \ 2 \ ieftiniri}[/tex]
