Question

Mihai are o suma de bani. Dupa ce dubleaza aceasta suma, cheltuieste 30 lei. Dubleaza suma ramasa si cheltuieste 20 lei. Dubleaza din nou suma ramasa si cheltuieste 160 lei. Mihai constata ca mai are 400 lei. Determina ce suma de bani a avut Mihai initial.

Answer 1

{[(a×2)-30]×2-20}×2-160=400
{[(a×2)-30]×2-20}×2=400+160=560
{[(a×2)-30]×2-20}=560:2=280
[(a×2)-30]×2=280+20=300
[(a×2)-30]=300:2=150
a×2=150+30=180
a=180:2
a=90