Question 1164916
You already saw solutions to examples like this done in two variables and two unknowns.  Here is what you could do to keep as just one single variable.


v liters of the 55%
15-v liters of the 40%

{{{55v+40(15-v)=50*15}}}
and solve for v, but simplify LATER.


{{{55v+40*15-40v=50*15}}}

{{{55v-40v=50*15-40*15}}}

{{{(55-40)v=15(50-40)}}}

{{{highlight_green(v=15((50-40)/(55-40)))}}}-------Think why this form is shown before simplifying it; and then computing v.  Then, evaluate 15-v.


You could do the solution as two equations and unknowns if you really want to.