Đáp án:
\(\begin{array}{l} m_{\text{dd NaCl (30%)}} = 150\ g.\end{array}\)
Giải thích các bước giải:
\(\begin{array}{l} \text{Gọi $m_{\text{dd NaCl (30%)}}$=a (g).}\\ \Rightarrow m_{NaCl\text{(30%)}}=a\times 30\%=0,3a\ (g).\\ n_{NaCl\text{(15%)}}=300\times 15\%=45\ g.\\ \Rightarrow \sum m_{NaCl}=0,3a+45\ (g).\\ \Rightarrow \sum m_{\text{dd NaCl}}=a+300\ (g).\\ \Rightarrow \dfrac{0,3a+45}{a+300}\times 100\%=20\%\\ \Leftrightarrow \dfrac{0,3a+45}{a+300}=0,2\\ \Leftrightarrow 0,3a+45=0,2a+60\\ \Leftrightarrow 0,1a=15\\ \Rightarrow a=150\ (g)\\ \text{Vậy $m_{\text{dd NaCl (30%)}}$ = 150 g.}\end{array}\)
chúc bạn học tốt!
