Question 945626
If your instruction shows or describes a preferred method, saying what it is could be helpful.


This can be reformed as concentrations of milk as fractions of each sample.


The concentrations of each sample are   {{{2/3}}}, {{{3/5}}}, {{{5/8}}}, {{{7/12}}}.  


Taking equal amount from each and combining these amounts means you have mixed 4 equal parts of the different milk concentrations.


{{{(2/3+3/5+5/8+7/12)/4}}}, the mixture fraction as milk.


The lowest denominator needed for handling the arithmetic is {{{3*5*8}}}.


{{{((2/3)(40/40)+(3/5)(24/24)+(7/12)(30/30))/4}}}


continue this;
you will have the resulting fraction of mixture as milk.  Change into the other ratio notation accordingly to finish.