Răspuns :
W (concentratia) = md x ms / 100
md = w x ms/100 = 60 x 500 / 100 = 300 g
ms = (md / w) x 100 = (300/30) x 100 = 1000 g
m apei = 1000 - 500 = 500 g este cantitatea de apa care trebuie aduagata peste solutie
ms1 = 500 g, c1 = 60%
ms2 = ? g , c2 = 30%
stim ca c% = mdx100/ms
notma cu a = masa de apa adaugata
md = ms1xc1/100 = 500x60/100 = 300 g
ms2 = mdx100/c2 = 300x100/30 = 1000 g sol finala
=> ms2 = ms1 + a => 1000 = 500 + a
=> a = 1000 - 500 = 500 g apa adaugata