To 200 g of an 8% sodium chloride solution was added 80 g of water. Mass fraction of salt in the resulting solution is equal to

In 200 g of an 8% solution of sodium chloride contains 200 * 0.08 = 16 g of sodium chloride
Therefore, its mass fraction in the final solution will be equal to:
16 * 100 / (200 + 80) = 5.7%

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