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3 mingi si 4 masinute costa impreuna 120 de lei . 5 mingi si 8 masinute costa 220 de lei. Cat costa o minge si cat costa o masinuta?

Răspuns :

x= mingi
y=masinute
3x+4y=120/·2
5x+8y=220
6x+8y=240
5x+8y=220

x=20lei 
100+8y=220
8y=120⇒y=15 lei