a+b+c=800. (mod algebric)
a=580
580+b+c=800
b+c=800-580
b+c=220
b-c=70=>b=c+70
c+70(b)+c=220
2c+70=220
2c=220-70
2c=150
c=75
b=75+70
b=145
a=580
(metoda prin reprezentare grafica)
a+b+c=800
a=580
580+b+c=800
b+c=220
b-c=70
b |—|--|<-70}220
c |—| }220
220-70=150(de 2 ori "c")
150:2=75(c)
75+70=145(b)
a=580