initial : suma = S
prima cheltuiala : S/2 a mai ramas (rest) : S/2
a 2-a " "" " " " "" 1/2 din S/2 = S/4 " " " " "" " "" " " " " S/2 - S/4 = S/4
a 3-a " " "" """"""1/4 din S/4 = S/16 " " " " " " " " " " """S/4 - S/16 = 3S/16
3S/16 = 819 lei ⇒ 3S = 819·16 S = 272·16 = 4352 lei