Water percent

A 15 g sample of the substance contains 70% water. After drying, the substance reduced the weight to 9 g. What percentage of water is now in the sample?

Correct answer:

p =  50 %

Step-by-step explanation:

$$\begin{gathered} m_1=15\text{ g } \\ q=70\mathrm{\%}={\displaystyle \frac{70}{100}}=0.7 \\ {m}_2=9\text{ g } \\ v=q\cdot m_1=0.7\cdot 15={\displaystyle \frac{21}{2}}=10.5\text{ g } \\ s=m_1-v=15-10.5={\displaystyle \frac{9}{2}}=4.5 \\ p=100\cdot {\displaystyle \frac{m_2-s}{m_2}}=100\cdot {\displaystyle \frac{9-4.5}{9}}=50\mathrm{\%} \end{gathered}$$

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