ms1 = 50g , c1% = 20%
ms2 = ? , c2% = 23%
stim ca c% = mdx100/ms
=> md1 = msxc1/100
= 50x20/100 = 10 g soda
md2 = md1 + a, a = masa de soda adaugata
=> ms2 = ms1 + a
=>
c2% = md2x100/ms2
=>
23 = 100(md1+a)/(ms1+a)
=> 50+a = 4,35(10+a)
=> a = 2 g soda adaugata