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Help.. Math Question

The order reads 40mg, you have 15mg in 5ml suspension. How many cc's?? Please tell me how you got this..



Specializes in Cardiac Telemetry/PCU, SNF.

The order reads 40mg, you have 15mg in 5ml suspension. How many cc's?? Please tell me how you got this..


Ok, I'll bite...

In reality it is simple stuff, perhaps only basic math, but I hope I can explain:

40mg is what you need, 15mg/5mL is what you have...

40mg * (5ml/15mg) = 13.3 mL

mg cancel, leaving you with mL, round the answer as needed, real basic calculations, should be in any nursing calculation book...



Let me try- I don't know how far along you are, so I'll say it anyway- cc's are the same as ML.

next, have you not done any dosage calculation yet?

then- we learned these as ratio/proportion problems, and it has always worked for me:

you have: 15mg:5ml::40mg:Xml

first part what you have, second part what you are looking for, both sides written the same, i.e. mg/ml&mg/ml. X is used to show what you are looking for. ::this symbol means is equal to.

Next step is multiply- if the above problem is said to have four components, we can call them A,B,C,D. If the X is in the D position, as it is above, then A is it's opposite, and in this first step you will leave that pair out. so you would start by multiplying 5ml by the 40mg, which is 200.

Next step is to divide, and you will divide the number you just came up with, 200, by the number that is left above, which is in the A position in this case. So, 200 divided by 15 = 13.33ml =X.

It took me along time in school to get this formula, but once I understood it it has never failed me. I have seen other students which were taught other ways of doing their calculations, and their answers are only right about half the time. This is a great formula.

Another way to say it: " I have this many mg in this many ml, (::) which is equal to this many mg in ?ml.

Let me know if none of this makes sense, O.K.?

I have no idea where that happy face came from, but a smile is always welcome, huh?

I like to reduce the concentration to milligrams per 1 ML (in this case 3mg/ml) then divide into total milligrams needed. 40mg divided by 3mg = 13.3 ml.


Specializes in Gerontological, cardiac, med-surg, peds.

I have included an attachment with Word document, showing how to work this out with Dimensional Analysis and Ratio Proportion.


loriangel14, RN

Specializes in Acute Care, Rehab, Palliative.

Using the dose over stock method you would divide 40 by 15 getting 2.666666. Round off to 2.7 and multiply by 5= 13.5. you would give 13.5 cc

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