Question

Mihaela, Costin si Cristina au împreună 160 lei. Calculati cati lei are fiecare daca Mihaela si Costin au impreuna 130 lei, iar Costin si Cristina au impreuna 80 lei.

Answer 1

x = Mihaela
y = Costin
z=Cristina
x+y+z=160
x+y=130 ⇒130+z=160⇒z=160-30=30lei⇒Cristina are 30 lei
y+z=80
z=30⇒y+30=80⇒y=80-30=50 lei⇒Costin are 50 lei
x+y+z=160
y+z=80⇒x+80=160⇒x=160-80=80⇒Mihaela are 80 lei

Answer 2

Vom nota numele copiilor cu litere : a = Mihaela
b = Costin
c=Cristina
⇒a+b+c=160 
⇒a+b=130 ⇒130+c=160⇒c=160-30=30 (de) lei⇒c=Cristina are 30 lei
⇒b+c=80
⇔c=30⇒b+30=80⇒b=80-30⇒50 (de) lei⇒b=Costin are 50 lei
⇔a+b+c=160
⇔b+c=80⇒a+80=160⇒a=160-80=80⇒a=Mihaela are 80(de) lei