Notăm: x-nr, carti literatura
y-nr carti matematica
x+y=10
9x+7y=76
inmultim prima ecuatie cu -7
-7x-7y=-70
9x+7y=76
Adunam cele doua ecuatii
2x=6
x=3
y=10-3=7
3, in prima zi 30S/100
in a doua zi 40S/100
in a treia zi 1S/4
a) a treia zi
b) S-(30S/100+40S/100+S/4)=100
S-95S/100=100
S=2000
