Fie a si b cele 2 nr.;
(a+b)+(a-b)=60; (a+b)-(a-b)=40; => a+b=40+(a-b)
; înlocuim : 40+(a-b)+(a-b)=60;
2 (a-b)=60-40; 2 (a-b)=20; a-b=20:2; a-b=10;
=>a+b=60-10; a+b=50; a-b=10;=>a=b+10;
Inlocuim: b+10+b=50;2b=50-10; 2b=40; b=40:2; b=20; =>a=50-20; a=30;
Verificare: (30+20)+(30-20)=50+10=60;
(30+20)-(30-20)=50-10=40