Question 1070952
Pure slime?  Not a recipe.  A recipe is something you eat.  Otherwise, it's a formula.


x gallons of the 20% slime
1000-x gallons of the 80% slime


{{{(20x+80(1000-x))/1000=65}}}


{{{(2x+8(1000-x))/100=65}}}


{{{x+4(1000-x)=50*65}}}


{{{x+4000-4x=3250}}}

{{{-3x=3250-4000}}}

{{{3x=4000-3250}}}

{{{highlight(x=250*gallons)}}}-------for the 20% slime, which leaves  750 gallons for the 80% slime.