20% din 300=0,2*300=60g substanta A
20% din 200=0,2*200=40g substanta B
A:B=60:40=3:2=1,5:1=> reactioneaza total ambele
comform legii conservarii maselor: mA+mB=mC+mD => 100g=mC+mD
msA=mdA+mH2O => mapa=300-60=240g apa
msB=mdB+mH2O => mapa=200-40=160g apa
mapasolutii=240+160=400g