SOLUTION: How many liters of 50% antiseptic solution must be added to 4 liters of a 20% solution in order to get a 30% antiseptic solution

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Question 817395: How many liters of 50% antiseptic solution must be added to 4 liters of a 20% solution in order to get a 30% antiseptic solution
Answer by josgarithmetic(39617) About Me  (Show Source):
You can put this solution on YOUR website!
{amount of antiseptic}/{amount of antiseptic solution}={concentration of resulting solution}
Let x = amount of the 50% solution to use, in LITERS.

highlight_green%28%2850x%2B4%2A20%29%2F%28x%2B4%29=30%29
Divide both sides by 10,
%285x%2B4%2A2%29%2F%28x%2B4%29=3
5x%2B8=3%28x%2B4%29
5x%2B8=3x%2B12
2x=12-8=4
highlight%28x=2%29