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Raluca are 200 de lei ,in bacnote de 10 si 5 lei.Daca are in total 28 de bacnote,aflati cate bacnote are?

Răspuns :

a -  banknote de 5

b-  banknote de 10

a+b=28  |-5
5a+10b=200

-5a-5b=-140
5a+10b=200

5a=60


a=12
b=16