A 36

A 36 g sample of the substance contains 91% water. After drying, the weight of the sample was reduced to 18 g. What percentage of water is now in the sample?

Correct answer:

p₂ =  82 %

Step-by-step explanation:

$$\begin{gathered} m_1=36\text{ g } \\ {p}_1=91\mathrm{\%}={\displaystyle \frac{91}{100}}=0.91 \\ {m}_2=18\text{ g } \\ s=m_1\cdot (1-p_1)=36\cdot (1-0.91)={\displaystyle \frac{81}{25}}=3.24\text{ g } \\ {w}_2=m_2-s=18-3.24={\displaystyle \frac{369}{25}}=14.76 \\ {p}_2=100\cdot {\displaystyle \frac{w_2}{m_2}}=100\cdot {\displaystyle \frac{14.76}{18}}=82\mathrm{\%} \end{gathered}$$

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