Question 1125628
Not the best example.  Concentrations of HCl above 40% not so practical; they don't keep well and will have some of the concentration lost quickly.




If you want the arithmetic anyway, then


x volume of 80%
1-x volume of 50%



{{{80x+50(1-x)=70*1}}}

{{{8x+5(1-x)=7}}}

{{{8x+5-5x=7}}}

{{{3x=7-5}}}

{{{3x=2}}}

{{{highlight(x=2/3)}}} liters of the 80% material

{{{highlight(1/3)}}} liters of the 50% material