Question 768935
More generally, a candy company mixes v pounds of H% fat content chocolate with u pounds of L% fat content chocolate to obtain M pounds of a T% fat content chocolate.   How many pounds of each type of chocolate should be used? 


The equations to that system are:
{{{highlight((Lu+Hv)/M=T)}}} and {{{highlight(u+v=M)}}}


You could try this way,
{{{Lu+Hv=MT}}}
{{{Hv=MT-Lu}}}
{{{v=(MT-Lu)/H}}}  and substitute this into the mass sum equation.

{{{u+(MT-Lu)/H=M}}}
{{{uH+MT-Lu=HM}}}
{{{uH-Lu+MT=HM}}}
{{{u(H-L)=HM-MT}}}
{{{u=(HM-MT)/(H-L)}}}
{{{highlight(u=M(H-T)/(H-L))}}}
...and you continue from there for getting v and later substituting values...