Răspuns:
m,impur= 125g
p= (100-20)%=80%
m,apa= 700g
c ?
calculez masa de sare pura
p=m,purx100/m,impur---> m,pur= 125x80/100g= 100g sare pura=md
calculez masa solutiei
ms= md+ m,apa= 100+700--> 800g
calculez c%
c= mdx100/ms= 100x100/800=12,5%
Explicație: