SOLUTION: constance Morgenstern is a chemist. she needs a 20% solution of alcohol. she has a 15% solution on hand, as well as a 30% solution. how many liters of the 15% solution should she a

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Question 27931: constance Morgenstern is a chemist. she needs a 20% solution of alcohol. she has a 15% solution on hand, as well as a 30% solution. how many liters of the 15% solution should she add to 3 liters of the 30% solution to get her 20% solution?
Answer by longjonsilver(2297) About Me  (Show Source):
You can put this solution on YOUR website!
look at my lesson on this topic on the algebra website.

Let x = number of litres of 15% solution required.

Question is all about "BEFORE mixing" equalling "AFTER mixing"

so BEFORE: xlitres of 15% + 3 litres of 30%
and AFTER: (x+3) litres of 20%

so... 0.15x + 0.30*3 = 0.20(x+3)
0.15x + 0.90 = 0.20x + 0.60
0.90 = 0.05x + 0.60
0.30 = 0.05x
--> x = 0.30/0.05
--> x = 6 litres

Jon.