SOLUTION: how many gallons of pure alcohol should be mixed with 20 gallons of 15% alcohol solution to obtain a mixture that is 25% alcohol?

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Question 336359: how many gallons of pure alcohol should be mixed with 20 gallons of 15% alcohol solution to obtain a mixture that is 25% alcohol?
Answer by Fombitz(32388) About Me  (Show Source):
You can put this solution on YOUR website!
Let A be the amount of 100% alcohol added.
100A%2B15%2820%29=25%28A%2B15%29
100A%2B300=25A%2B375
75A=75
A=1
One gallon of pure alcohol needs to be added.