SAT Mathematics Practice Test 6

The total amount, in liters, of a saline solution can be expressed as the liters of each type of saline solution multiplied by the percent of the saline solution. This gives $3\left(0.10\right),\mathit{x}\left(0.25\right),$ and $\left(\mathit{x}+3\right)\left(0.15\right),$ where $\mathit{x}$ is the amount, in liters, of a $25\%$ saline solution and $10\%,15\%,$ and $25\%$ are represented as $0.10,0.15,$ and $0.25,$ respectively. Thus, the equation $3\left(0.10\right)+0.25\mathit{x}=0.15\left(\mathit{x}+3\right)$ must be true. Multiplying 3 by $0.10$ and distributing $0.15$ to $\left(\mathit{x}+3\right)$ yields $0.30+0.25\mathit{x}=0.15\mathit{x}+0.45.$ Subtracting $0.15\mathit{x}$ and $0.30$ from each side of theequation gives $0.10\mathit{x}=0.15$. Dividing each side of the equation by $0.10$ yields $\mathit{x}=1.5$, or $\mathit{x}=\frac{3}{2}$