Question 1160428
{{{0.5*35/(v+35)=0.05}}}

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This will help but is usually not necessary:
<pre>
MATERIAL           CONCENTRATION (as fraction)      VOLUME

50% Alcohol                    0.5                   35

Water                          0.0                    v

5% Solution                   0.05                  v+35
   Result
</pre>
Result wanted is  {{{0.05=(alcoholquantity)/(totalvolume)}}}


{{{0.05=(0.5*35)/(v+35)}}}

This is clear enough.  Solve for v.