Tricky pharmacy math Problem

by Heidi
(Austin, Texas)

Can you show me the math for this question:

Which of the following formulas will produce a 1000ml solution of 3.5% amino acid in 15% dextrose?

A) Amino Acid 10% 500ml + dextrose 30% 500ml


B) Amino Acid 10% 300ml + dextrose 30% 500ml


C) Amino Acid  7% 500ml  + dextrose 30% 500ml


D) Amino Acid  7% 400ml  + dextrose 30% 600ml



Reply: (Keith) This looks like a tricky question, but it's actually an easy one once you think about what's going on. What you need to do is first think about the two solutions you are mixing together.

Now, the dextrose solution will be diluting the amino acid solution the very same as if you were adding water. The same is true about the amino acid solution diluting the dextrose.

That said, ask yourself : in a 1000ml solution, how much amino acid would it take to obtain a 3.5% solution if I was just mixing with water. Look at the available choices. The one in answer "C" is the only one that would make that work.

Then ask yourself : in a 1000ml solution, how much Dextrose would it take to obtain a 15% solution if I was just mixing with water. Look at the available choices. The ones in answers "A, B and C" would make that work.

The answer has to be "C"

To rephrase all of this, lets suppose the Question was asking:
Which of the following would be best to produce a 1000ml solution of 3.5% amino acid... and then the same for the Dextrose.

By the way,
Excellent question! these are some of the kind of questions you need to prepare for.

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Tricky pharmacy math Problem

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May 28, 2011
Easier way when you don't have too much time
by: Anonymous

When I see a problem like this one I take the larger percentage and divide that by the smaller one. Then I do the same thing with the answers given percentages. Which ever one that matches is the right answer. Also don't forget the volume has to match.
Like for example this problem. Do these steps.

15:3.5=4.28
30:7=4.28
Then just make sure the volume totals 1000ml.

Answer C

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