SOLUTION: To the nearest mL, how much 0.3% ampicillin in solution do you have to add to 40 mL of 0.5% ampicillin in solution to create 0.4% ampicillin in solution?

Question 726776: To the nearest mL, how much 0.3% ampicillin in solution do you have to add to 40 mL of 0.5% ampicillin in solution to create 0.4% ampicillin in solution?
Answer by Alan3354(69443) (Show Source): You can put this solution on YOUR website!
To the nearest mL, how much 0.3% ampicillin in solution do you have to add to 40 mL of 0.5% ampicillin in solution to create 0.4% ampicillin in solution?
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Since 0.4 is the average of 0.5 & 0.3, it's an equal amount = 40 ml
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40*0.5 + x*0.3 = (40 + x)*0.4
40*5 + 3x = 4*(40 + x)
200 + 3x = 160 + 4x
x = 40 ml of 0.3%
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