A chemist wishes to make 10 gallons of a $15 \%$ acid solution by mixing a $10 \%$ acid solution with a $25 \%$ acid solution.
(a) Let $x$ and $y$ denote the total volumes (in gallons) of the $10 \%$ and $25 \%$ solutions, respectively. Using the variables $x$ and $y,$ write an equation for the total volume of the $15 \%$ solution (the mixture).
(b) Using the variables $x$ and $y,$ write an equation for the total volume of acid in the mixture by noting that
Volume of acid in $15 \%$ solution $=$ volume of acid in $10 \%$ solution $+$ volume of acid in $25 \%$ solution.
(c) Solve the system of equations from parts (a) and (b), and interpret your solution.
(d) Is it possible to obtain a $5 \%$ acid solution by mixing a $10 \%$ solution with a $25 \%$ solution? Explain without solving any equations.