x=suma initiala
2x/5=ziua 1
x-2x/5=3x/5=rest
3x/5 × 3/7=9x/35=ziua 2
3x/5-9x/35=(21x-9x)/35= 12x/35=rest
12x/35 ×2/3=8x/35=ziua 3
9x/35-3=8x/35
9x-105=8x
x=105 lei suma initiala
ziua 1 105 × 2/5=42 lei
rest 105-42=63 lei
ziua 2 63 × 3/7=27 lei
rest 63-27=36 lei
ziua 3 36 × 2/3=24 lei
rest 36-24=12 lei