Notam: cartile Alinei - x; ale Cristinei - y; ale Veronicai - z
• x+y+z = 678
• x+y = 421 <=>
• y+z = 492
• x+y+z = 678
• x = 421-y <=>
• z = 492-y
• 421-y+y+482-y = 678
• x = 421-y <=>
• z = 492-y
• 913-y = 678
• x = 421-y <=>
• z = 492-y
• y = 913-678 = 235
• x = 421-235 = 186
• z = 492-234 = 257
Alina - 186 carti
Cristina - 235 carti
Veronica - 257 carti
(Fiecare 3 puncte le pui intr-un sistem)