Question 709360
Mixing two different concentrations of solution.  Quantity of one solution is known but quantity of the other solution is unknown.  One variable as unknown is expected; only one.

Let y = how many gallons of the high concentration solution to add.


{{{highlight((90y+25*80)/(80+y)=80)}}}
(important to know the actual units in use and do not become confused with the double occurrance of "80". One is for a quantity of antifreeze and the other is a resulting concentration as percent.)


Solve for y in that rational equation.