Răspuns :
[tex]\displaystyle\\ x = \text{numarul elevilor din clasa.}\\\\ \frac{1}{4}\cdot x =\frac{x}{4} = \text{numarul elevilor care merg la cercul de matematica.}\\\\ x - \frac{x}{4} = \frac{3x}{4} = \text{restul elevilor care NU merg la cercul de matematica.}\\\\ \frac{1}{4}\cdot \frac{3x}{4} =\frac{3x}{16} =\text{numarul elevilor care merg la cercul de informatica.}\\\\ 18 = \text{Restul elevilor care merg la cor.}\\\\ [/tex]
[tex]\displaystyle\\ x = \frac{x}{4}+\frac{3x}{16} +18~~~\Big|~\cdot 16\\\\ 16x = \frac{16x}{4}+\frac{16\cdot 3x}{16} +16\cdot 18\\\\ 16x = 4x+3x+16\cdot 18\\\\ 16x - 4x-3x=16\cdot 18\\\\ 9x = 16\cdot 18\\\\ x = \frac{16\cdot 18}{9} = 16\cdot 2 = \boxed{\bf 32~~\text{\bf de elevi sunt in clasa.}}[/tex]
