Question 788849
{pure alcohol content}/{total amount of solution}={Target Concentration}


u = amount of the water which is 0% alcohol
v = amount of the 25% alcohol


{{{25*v/(u+v)=5}}} and {{{u+v=325}}}


{{{v=325-u}}} and substitute into the rational equation.
{{{25(325-u)=5(u+325-u)}}}
{{{25*325-25u=5*325}}}
{{{25*325=5*325+25u}}}
{{{25*325-5*325=25u}}}
{{{325(25-5)=25u}}}
{{{20*325=25u}}}
{{{25u=20*13*25}}}
{{{u=20*13}}}
{{{highlight(u=260)}}} mL.


Steps can vary.  Some people's steps may be more efficient than shown here.  Using factors and making more steps was easier here to avoid using separate computations on paper for simplifications.