SOLUTION: How many gallons of a 90% antifreeze solution must be mixed with 80 gallons of 25% antifreeze to get a mixture that is 80% antifreeze?

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Question 709360: How many gallons of a 90% antifreeze solution must be mixed with 80 gallons of 25% antifreeze to get a mixture that is 80% antifreeze?
Answer by josgarithmetic(39617) About Me  (Show Source):
You can put this solution on YOUR website!
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%28%2890y%2B25%2A80%29%2F%2880%2By%29=80%29
(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.