Question

Peste 400g solutie NaCl se adauga 200g apa.Concentratia solutiei devine 20%.Concentratia procentala a solutiei initiale este ...?

Answer 1

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

Concentratia initiala este de 30 la suta

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