x= gramajul de NaCl
[tex] \frac{x}{200+400} = \frac{x}{600}= \frac{20}{100} [/tex]
[tex] \frac{x}{600} = \frac{2}{10} [/tex]⇒x=[tex] \frac{600x2}{10} = 60x2=12(grame)
cantitatea de NaCl ramane aceeasi, deci concentratia initiala este
[tex]c= \frac{120}{400} x100 = \frac{12}{40} x100 = \frac{3}{10} x100=30[/tex]
Concentratia initiala este de 30 la suta
Spor la teme! :)
