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Literina a economisit 64 lei in bacnote de 1 leu si de 5 lei. Are 20 de bacnote.

Răspuns :

x+5y=64;
x+y=20;
⇒x=20-y;
⇒20-y+5y=64
⇒20+4y=64⇒4y=44⇒y=11[bancnote de 5 lei];
⇒x=9[bancnote de 1 leu];