Great job! I too was really nervous about my dosage calc test. Passed it, so I'm happy. I think dimensional analysis is great. Once I figured it out I realized how simple it is compared to the other methods. Plus, I don't have to remember a formula.
This is how I do dimensional analysis. By the way, this is a question from the book Dosage Calculations Made Incredibly Easy!, which I highly recommend if you (as in, the person in the online abyss reading this right now) are having problems with dosage calculations.
A patient is to receive 50 mcg of levothyroxine (Synthroid). The drug is available as 200 mcg per 5 ml. How many milliliters should the nurse prepare?
First, figure out what the the question is asking. How many milliliters? Start setting up the equation.
Now, what quantities does the problem give us?
50 mcg and 200 mcg/ 5 ml
I always set up the equation putting what I need to end up with first. So, since I need to end up with milliliters I will put milliliters (5 ml/200 mcg)right after the equal sign.
ml = 5 ml/200 mcg
Now I have to figure out how to get rid of that mcg since I only need to end up with ml. The only quantity I have left is 50 mcg.
ml = 5 ml/200 mcg x 50 mcg
Cancel out the mcg and do a bit of math and you get 1.3 ml.
It's just easier for me to remember that if I need, say, mg when I'm all done then I need to write mg = ___ mg/_____ x _____.
So it doesn't matter what you're calculating, whether it's drip rates, number of tablets, or dosages. Just start with what you need and on the other side of the equal sign start with that same unit. So if you need gtts/min you write out gtts/min = ___ gtts/______ x _____.
It is hard to explain this in writing!