Question 730609
Before adjustment, 11.0 liters of mixture is in the system and after adjustment, still 11.0 liters of mixture is in the system.  Give a variable, say, q, for how much material to remove and how much pure antifreeze to add.  


(pure antifreeze ingredient)/(antifreeze solution)=25%, what's wanted.


You want to adjust from 15% to 25%.


{{{(11.0*15-q*15+q*100)/(11.0)=25}}}
Think to understand how that makes sense.


.
The steps should lead to {{{11*15+(100-15)q=25*11}}}
.
{{{q=11*(10)/85}}}
{{{q=1.29}}}