Solution Mixture Math - Basic Algebra

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There are a few ways to calculate the resulting percentage strength when combining two different strengths of the same type of solution. The examples here are only for the purpose of studying for the PTCB or ICPT national exams. Do not use the instructions on this page or website in a professional setting or for compounding actual solutions. Please refer to the method your supervising pharmacist issues in a professional environment.

Let's first look at a short video, then an example / practice question
similar to what you might find on the pharmacy Tech Test:

Watch this basic algebra primer video





Includes:
· Proportions Math
· Cross Multiplication
· C1V1 = C2V2
· Solution Mixtures



Practice Question:


You have been asked to take 1.5L / 20% strength solution and combine it into 3.0L / 12.5% strength of the same type of solution. When finished, you will have 4.5L of the solution, but, what percent ?

A. 18%

B. 15%

C. 13%

D. 10%



Organize your known information:

%
 Decimal
Qty.
Set-up
Have
20%
.20
1500ml
1500(.20)
Have
12.5%
.125
3000ml
3000(.125)
Unknown
?
"X"
4500ml
4500(X)


1) The Equation Set-up:

1500(.20) + 3000 (.125) = 4500X



2) Do the math:

1500(.20) + 3000 (.125) = 4500X

      300      +         375        = 4500X

                 675                     = 4500X



3) Isolate for "X":

675
    =    
4500x
       
4500
        
4500  




4) Solution:

    0.15   =   X


    You end up with a 15% solution




Solution Mixture Video Tutorial
by Zita Schmitt, CPhT









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