datele problemei
f+s+z+u=800
s=f-180=z+40
u=s/7
rezolvare
din s=f-180 rezulta f=s+180
din s=z+40 rezulta z=s-40
si u=s/7
inlocuim in relatia f+s+z+u=800
s+180+s+s-40+s/7=800
3s+s/7+140=800
(21s+s)/7=800-140
22s/7=660
s=(7·660)/22
s=210 g are smantana
f=s+180=210+180=390
f=390 g are faina
z=s-40=210-40=170
z=170g are zaharul
u=s/7=210/7=30
u=30 g are untul
210+390+170+30=800