Răspuns :
x=suma initiala pe care o avea coplilul\
3|7din banii=600
3|7×x=600⇒3x|7=600⇒3x=7x600⇒3x=4200⇒x=4200|3⇒x=1400
proba
3|7x1400=4200|7=600
succes!
3|7din banii=600
3|7×x=600⇒3x|7=600⇒3x=7x600⇒3x=4200⇒x=4200|3⇒x=1400
proba
3|7x1400=4200|7=600
succes!