<PRE><B>Question 1203535</B>
The problem can be done all in variables, but seems easier to handle using a table of data.
&lt;pre&gt;
MATERIAL CONC.%         VOLUME         AMOUNT PURE
         22              100             22*100
        100               v              100v
         70              v+100           70(v+100)
&lt;/pre&gt;

Question asks for how much of the pure 100% alcohol to add, v.


Accounting for the amount of alcohol for the separate parts,
{{{100v+22*100=70(v+100)}}}


{{{100v+22*100=70v+70*100}}}

{{{(100-70)v=70*100-22*100}}}

{{{v=100((70-22)/(100-70))}}}-------simplify and compute.

{{{v=100(48/30)}}}

{{{v=100(1.6)}}}

{{{highlight(v=160)}}}---------ml. of the pure 100% alcohol to use</PRE>