Răspuns:
Explicație:
100 g solutie 10%............10 g soda..................90 g apa
200 g..................................20 g soda.................180 g apa
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100 g solutie 20%..................20 g soda..................80 g apa
x ................................180 g apa
x = 180*20/80 = 45 g soda
45 - 20 = 25 g soda trebuie adaugata
