Molarity Numerical on Mixing Solutions If 3 L of 1 M NaOH solution is prepared by mixing properties of stock solutions of $x$ L of 2.5 M NaOH and $y$ L of 0.4 M NaOH and no water is to be used, find $x : y$.


My attempt:

$$3 = 2.5x + 0.4y$$

Now I am stuck how to calculate $x:y$.
In addition to the equation for the preservation of the amount of substance you've written, there is one more equation you can use for the system, namely the one reflecting preservation of volumes: $x + y = 3$:

$$
\left\{ 
\begin{align}
x + y &amp;= 3 \\ 
2.5x + 0.4y &amp;= 3 
\end{align}
\right. 
$$

$$x + y = 2.5x + 0.4y$$

$$1.5x = 0.6y$$

$$\frac{x}{y} = \frac{6\cdot 2}{10\cdot 3} = \frac{2}{5}$$

E.g. the answer is $x : y = 1 : 2.5$.