Question 977523
See here:  <a href="http://www.algebra.com/my/Mixtures%3A-All-in-Symbols.lesson?content_action=show_dev">http://www.algebra.com/my/Mixtures%3A-All-in-Symbols.lesson?content_action=show_dev</a>


You can also handle this in one single variable like this:
v, how much 8% alcohol to use
M-v, how much 15% alcohol to use
M=82
T=13.9
L=8
H=15
-
-
{{{highlight_green((Lv+H(M-v))/M=T)}}}
{{{Lv+HM-Hv=MT}}}
{{{Lv-Hv+HM=MT}}}
{{{(L-H)v=MT-HM}}}
{{{v=(MT-HM)/(L-H)}}}
and because you know L<H, you want to multiply by  {{{(-1)/(-1)}}}.
{{{highlight(v=(HM-TM)/(H-L))}}}
-
Now just substitute the values for H, M, T, and evaluate v.