<PRE><B>Question 1193722</B>
500 L of 2.5% additive
x Liters of the 7.5% additive
Mixture result 6.5% additive


Account for the amount of the pure additive.
{{{2.5*500+7.5x=6.5(x+500)}}}
Solve!


Do all computations LAST.


{{{7.5x+2.5*500=6.5x+6.5*500}}}
{{{7.5x-6.5x=6.5*500-2.5*500}}}

{{{(7.5-6.5)x=500(6.5-2.5)}}}

{{{highlight_green(x=500((6.5-2.5)/(7.5-6.5)))}}}

{{{x=500(4/1)}}}


{{{highlight(x=2000)}}}


CHECK - Does this value work?

{{{2.5*500+7.5*2000=6.5(2500)}}}
{{{1250+15000=16250}}}
{{{16250=16250}}}
YES</PRE>