Răspuns:
c=20%
Explicație:
ms1=200g sol.
c1=40%
ms2= 300g sol. soda de rufe
c2=20 %
c totala
-se afla md1 si md2
md1= c1 . ms1 : 100
md1= 40 .200 : 100=80 g soda
md2= c2 . ms2 :100
md2= 20 . 300 : 100=60g soda
-se afla md final
mdf= md1 + md2
mdf= 80 + 60=140g soda
-se afla ms final
msf= ms1 + ms2
msf=200 + 300=500g sol.
c= 140. 100 : 500= 28%