x-prețul unui caiet
y-prețul unei truse de geometrie
[tex] \left \{ {{3x+5y=142} \atop {3x-2=2y}} \right.⇔ \left \{ {{3x=142-5y} \atop {142-5y-2=2y}} \right.⇔ \left \{ {{3x=142-5y} \atop {-5y-2y=-142+2}} \right.⇔ \left \{ {{3x=142-5y} \atop {-7y=-140}} \right. ⇔ \left \{ {{3x=142-5y} \atop {7y=140}} \right.⇔ [/tex][tex] \left \{ {3x=142-5y} \atop {y=20}} \right. ⇔ \left \{ {{3x=142-5*20} \atop {y=20}} \right. ⇔ \left \{ {{3x=142-100} \atop {y=20}} \right.⇔ \left \{ {{3x=42} \atop {y=20}} \right. ⇔ \left \{ {{x=42:3} \atop {y=20}} \right. ⇔ \left \{ {{x=14} \atop {y=20}} \right. [/tex]
3·14+5·20=42+100=142 (A)
Raspuns: x=14, y=20.
