ms1 = 120 g , c1 = 40%
c2 = 25%
c% = mdx100/ms
=> md = ms1xc1/100 = 120x40/100 = 48 g
notam cu a = masa de apa adaugata
ms2 = ms1 + a = 120+a
c%final = mdx100/ms.final
=> 25 = 48x100/(120+a)
=> a = 1800/25 = 72 g apa adaugata
facem proba
ms.final = 120+72 = 192 g
md = 48 g
=> c% = 48x100/192 = 25%, deci verifica calculele de mai sus
