solution to #20 on bonus PTCB practice quiz 5

by Darcetha

Hello. As usual, I was over analyzing question 20 on the
Bonus free practice quiz 5(Opens in new window)

After putting it down and coming back to look at it, I finally figured out what I was doing wrong.

Question 20 wanted to know if 350ml of SWI is added to 75ml of an 85% stock solution, what is the percentage strength of the resulting solution?

In order to solve this problem, one would use the pharmacy dilution formula, which is C1V1=C2V2.

C1=concentration of solution 1
V1=volume of solution 1
C2=concentration of solution 2
V2=volume of solution 2

Using the above formula, you would put in the following numbers:



Divide both sides by 52.5 to get the answer 1.214.

So, the answer to this question is (B) or 15%.

Reply (Keith)

You're on the right track, but forgot to put in your unknown.

The setup would go like this:

350(.00)+75(.85) = 425(X)

63.75 = 425X
----- = -----
  425     425

X = 0.15

Comments for
solution to #20 on bonus PTCB practice quiz 5

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Mar 23, 2012
How do you get the 425?
by: Buddy

Reading the question it tells you that you add 350ml to 75ml. Those numbers added together will render an answer of 425.

Jul 30, 2011
Response to question by Bonnie
by: Darcetha

Hello, Bonnie. In response to your question, about wanting to see more math formula questions sent to you, my suggestion would be to Google nursing math or nursing drug calculations. You will find tons of websites that cover IV drug calculations, drug calculations based on weight, etc. I found that to be helpful for me while I study. :)

Jul 30, 2011
Don't get You
by: Anonymous

How did you get the 425

Jul 28, 2011
I don't understand
by: Anonymous

I don't understand the difference in when you would use the (OV)(OS)= (NV)(NS) apart from when you would use (OV1)(OS1)+ (OV2)(OS2) = (NS)(NV) its so frustrating because i tried this problem using the first formula and got it wrong, can someone explain the diffrence and when to use which?

Jun 23, 2011
by: Anonymous

Thanks for the answer to this question because I was stuck on this one as well.

May 30, 2011


May 27, 2011
Thanks Keith
by: Darcetha

Thanks Keith for your vote of confidence! I'm learning and constructive criticism is also helpful, as long as it is not demeaning of a person. Your site is great for those of us who are not in the medical field or don't have lots of math experience.

Thanks again!

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