Răspuns :
[tex]x+3y=300 \\ x-y=20 \\ x=20+y \\ 20+y+3y=300 \\ 4y=300-20 \\ 4y=280 \\ y=280:4 \\ \boxed{y=70} \\ x=20+y=20+70 \\ \boxed{x=90}[/tex]
Notam cele 2 nr cu x si y
x+3y=300
x-y=20 => x=20+y
20+y+3y=300 => 20+4y=300 => 4y=280 => y=70
x=20+70 => x=90
x+3y=300
x-y=20 => x=20+y
20+y+3y=300 => 20+4y=300 => 4y=280 => y=70
x=20+70 => x=90