ms=500g
c=20%
c= mdx100/ms= mdx100/(md+m,apa)
20 md
---- = ---------> md= 100g aceasta masa se afla, dupa evaporarea apei in
100 500 ms= 400g sol
c= mdx100/ ms
c= 100x100/ 400=.....................calculeaza, trebuie sa rezulte mai mare decat concentratia initiala