Sea water

Seawater contains about 4.3% salt. How many dm³ of distilled water we must pour into 5 dm³ of sea water to get water with 1.8% salt?

Correct answer:

V =  6.94 dm³

Step-by-step explanation:

$$\begin{gathered} 4.3\mathrm{\%}\cdot 5=1.8\mathrm{\%}\cdot (5+V) \\ 4.3\mathrm{/}100\cdot 5=1.8\mathrm{/}100\cdot (5+V) \\ 4.3\cdot 5=1.8\cdot (5+V) \\ 1.8V=12.5 \\ V={\displaystyle \frac{125}{18}}\doteq 6.944444={\displaystyle \frac{125}{18}}{\text{dm}}^3=6.94{\text{dm}}^3 \end{gathered}$$

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