SOLUTION: How much pure alcohol should be added to a 40% alcohol solution to make 600mL of a 75%alcohol solution? (equations please)

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Question 857987: How much pure alcohol should be added to a 40% alcohol solution to make 600mL of a 75%alcohol solution? (equations please)
Found 2 solutions by fcabanski, Alan3354:
Answer by fcabanski(1391) About Me  (Show Source):
You can put this solution on YOUR website!
We have to know how much there is of the 40% solution.

Answer by Alan3354(69443) About Me  (Show Source):
You can put this solution on YOUR website!
How much pure alcohol should be added to a 40% alcohol solution to make 600mL of a 75%alcohol solution?
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p = pure
f = 40%
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100p + 40f = 600*75 (total solution)
p + f = 600 (total alcohol)
f = 600 - p
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100p + 40*(600-p) = 45000
10p + 2400 - 4p = 4500
6p = 2100
p = 350 ml
f = 250 ml