SOLUTION: To the nearest mL, how much 0.3% ampicillin in solution do you have to add to 40mL of 0.8% ampicillin in solution to have 0.4 mL ampicillin total?

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Question 626541: To the nearest mL, how much 0.3% ampicillin in solution do you have to add to 40mL of 0.8% ampicillin in solution to have 0.4 mL ampicillin total?
Found 2 solutions by stanbon, lwsshak3:
Answer by stanbon(75887) About Me  (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 40mL of 0.8% ampicillin in solution to have 0.4 mL ampicillin total?
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Equation:
amp + amp = amp
0.003x + 0.008*40 = 0.4
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Multiply thru by 1000 to get:
3x + 8*40 = 400
3x = 80
x = 26 2/3 mL (amt of 0.3% amp needed)
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Cheers,
Stan H.

Answer by lwsshak3(11628) About Me  (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 40mL of 0.8% ampicillin in solution to have 0.4% mL ampicillin total?
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let x=amt of .3% ampicillan to add
.3%x+.8%*40=.4%(40+x)
.003x+.32=.16+.004x
.001x=.16
x=.16/.001
x=160
amt of .3% ampicillan to add=160 ml