Question 745672
So you have 10 cc of 30% acid, and you want to add water to get 6% acid.

Let v = the volume of water to add.


{{{(10*30+v*0)/(10+v)=6}}}
Notice that the v of water gives no acid so the factor with v is zero.
Same as saying {{{(10*30)/(10+v)=6}}}.  Just solve for v.