SOLUTION: a test solution of gasohol contains 60L of gasoline and 15L of alcohol. How much pure alcohol must be added so that the resulting solution is 25% alcohol?

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Question 9442: a test solution of gasohol contains 60L of gasoline and 15L of alcohol. How much pure alcohol must be added so that the resulting solution is 25% alcohol?
Answer by rapaljer(4551) (Show Source):
You can put this solution on YOUR website!
Let x = amount of pure alcohol that must be added

Total liquid = 60+15 + x= 75+x

Amount of pure alcohol before = Amount of pure alcohol after
15 + x = .25(75 + x)
15 + x = 18.75 + .25x

Subtract .25x from each side:
15 + x - .25x = 18.75 + .25x - .25x
15 + .75x = 18.75

Subtract 15 from each side:
15-15 + .75x = 18.75 - 15
.75x = 3.75

Divide both sides by .75
liters

Check: Total alcohol = 15L + 5L = 20 L
Total mixture = 60L + 15L + 5L = 80L,
Mixture is 20/80 % or 25% alcohol.

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