Looking at the W/V formula, we know we need to reduce the fraction by half in this case in order to make our denominator go from 200ml - 100ml:1.50g ÷ 2
200ml ÷ 2
5)Now, our converted fraction is:
6)Now look at the numerator ! Our answer is 0.75% W/V. Now that you have the (bottom) denominator at 100ml, whatever is in the (top) numerator is your % W/V.
-Don't let the decimals fool you. If you saw a 1 in the numerator, it would be 1%, right ?
-As you get better at this, you'll see that it's all about getting your fraction setup properly and then getting your denominator to 100ml.
That's really the basic rundown on Concentration Percentage as it's used in Pharmacy Tech Math. Whatever program you are studying will likely have a much more detailed approach and several practice problems.
The next step in learning about compounding math is learning about using Alligations, which are used when mixing a preparation of a certain percentage when you have two different strengths to work with. Whatever you do, don't confuse the formulas we have done here with Alligations. You will know distinctly to use an Alligationwhen the question says you have two different strengthsto work with.
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Go to Alligations Page
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Next, take the volume of Drug "Q" and divide it by the total volume.
90 ÷ 690 = .13**
Lastly, you can either move the decimal two places or multiply by 100.
.13 → 13.
.13 X 100 = 13
Answer is: 13% V/V
**Side note - For the purpose of studying for the PTCB or ExCPT exams, round all decimals to the nearest hundredth. If your calculator says 0.130434 then go with .13
The example we did will work to determine what a Concentration Percentage is. However, what if we were asked the question this way:
(or move the decimal over two places).
13 ÷ 100 = .13
Then, multiply the desired total volume by that.
690 X .13 = 90
Answer is: 90mL
We know the answer is correct by looking at the previous question and answer.
Question From Jennifer on Yahoo Answers:
1) The first thing I like to do is get those milligrams turned into Grams since the W/V formula is 1g/100mL. We'll do that by multiplying our fraction by 10.
150mg x 10 = 1500mg (1.5g)
20ml x 10 = 200mL
2)Next, convert the 1500mg to grams. Now your fraction is:
3)Now, remember the W/V formula: