The Nursing Math Thread

All I can say is on a bag of 1/2 normal saline it says 0.45% so yeah it's half of 0.9%. Still in DA you cancel terms so the answer can only be % or mL if you set it up with those terms. So if 0.9% is 3.2g then 0.45% would be 1.6g in 1L of fluid.

1.6g x 700mL = 1120 = 1.12g/700mL ( or 0.7L)

1000mL...1.......1000

Thank you again, that does seems to make it a bit more clear...At least now I can tell where the half is being subtracted from :)..and on that site they have the answers in that section all set up to come out to grams for some reason( http://www.dosagehelp.com/practice_questions?answer=1.89+g&question_type=2 ) and I am very new so I wasn't quite sure why.........I have learned enough to know that you have to cancel out the terms on the top and bottom that you don't want and do conversions to like terms when needed. I think I have a decent grasp of DA so far....and then snags like this come along.

You'll get it...DA still trips me up too sometimes:lol2: that's the great thing about this site you can usually find someone who can see the way it fits, if it's unclear! I am using this as practice to get ready for my 3rd semester math test in about 3 weeks, helping others helps me learn too! Good luck and post again anytime you need help!

beth,

I am thinking that since they are looking for the NaCl in that question they are looking for grams to determine how much dry/powdered NaCl went into the Normal Saline to reconstitute it...so that is where the grams come in and why that is what's being solved for instead of percent or mL. So there would still need to be a conversion from mL to grams in there somewhere.

Best of luck on your test:nurse:

Here is the problem...

Calculate amount of sodium chloride in 0.7 L 1/2 NS.

I can do it in the formula way (I think that's what it's called)

50% X 0.9% x700ml = 3.15 g or 3.2g

---------------------

100

Okay......I ended up coming up with the same answer using DA (a short cut version since I am not sure how to put the changing of the % to DA that came up with the .45 that was mentioned above)

So this is what I came up with...

700ml .45 = 315

------ x ------- ------ or 3.15 or 3.2 grams of NaCl

100 ml 100

.45 being the sum of 0.9% X .5%

Any idea how that would look in DA? Would it be 0.9 %/100 and .5%/ 100 since percent is 100?

Okay......I ended up coming up with the same answer using DA (a short cut version since I am not sure how to put the changing of the % to DA that came up with the .45 that was mentioned above)

So this is what I came up with...

700ml .45 = 315

------ x ------- ------ or 3.15 or 3.2 grams of NaCl

100 ml 100

.45 being the sum of 0.9% X .5%

Any idea how that would look in DA? Would it be 0.9 %/100 and .5%/ 100 since percent is 100?

Maybe like this?

I am assuming that the .9 is grams of NaCl being added to the 1/2 (.5) NS to make up the 100% that is the solution.

700ml .9 g. x .5 NS = 315

------- X --------- ------ = 3.2 grams

100ml 100

Maybe like this?

I am assuming that the .9 is grams of NaCl being added to the 1/2 (.5) NS to make up the 100% that is the solution.

700ml .9 g. x .5 NS = 315

------- X --------- ------ = 3.2 grams

100ml 100

I'm really not sure why you keep trying to put the % in the problem, if you know how many grams you add to get a solution of 0.9% NaCl you use the grams. I have never done a DA problem with %. The original problem you posted ask for an amount of NaCl to be added not the percentage. In all your coversion fators there is not one for % so you can't break it down. The percentage of a med or solution is going to be mg. g, mL, L, oz, tsp, etc. 30% of a syringe is measured as so many mL. The 0.9 solution or NS is so many mg or grams of NaCl in water, and 1/2 NS is 1/2 that many grams or mg of NaCl in water, so you need to use those units of measure not %. Does this make sense?:)

I'm really not sure why you keep trying to put the % in the problem, if you know how many grams you add to get a solution of 0.9% NaCl you use the grams. I have never done a DA problem with %. The original problem you posted ask for an amount of NaCl to be added not the percentage. In all your coversion fators there is not one for % so you can't break it down. The percentage of a med or solution is going to be mg. g, mL, L, oz, tsp, etc. 30% of a syringe is measured as so many mL. The 0.9 solution or NS is so many mg or grams of NaCl in water, and 1/2 NS is 1/2 that many grams or mg of NaCl in water, so you need to use those units of measure not %. Does this make sense?:)

Beth,

I am not trying to put the percent into the problem or to be contrary...the way it is written on www.dosagehelp.com is what I posted previously, that 0.9% is the amount in NS..I copied that from their site as well as the question......and if there is 1/2 NS, then that is also 50% NS....or 0.5 which is why in my part of the problem that you quoted above I put the 0.5 and the 0.9 over 100, which they are both a part of the whole....or a percent of the whole 100....

The way you have explained it above does give me some clarity on a couple of things, but I am just going by how that particular site worded it, and those two numbers are intergral to getting the correct answer. I do see now that what I read there as percent is also grams/whole in the case of NS.

According to the site, which doesn't teach DA (they use formula), I have the correct answer in the 3.2g........and the way I found that I could put it in a DA formula is what I have above, and it comes out to the correct answer.

Basically, I think, I answered my own original question which was how to put that particular question into DA and get the correct answer.

I'm really not sure why you keep trying to put the % in the problem, if you know how many grams you add to get a solution of 0.9% NaCl you use the grams. I have never done a DA problem with %. The original problem you posted ask for an amount of NaCl to be added not the percentage. In all your coversion fators there is not one for % so you can't break it down. The percentage of a med or solution is going to be mg. g, mL, L, oz, tsp, etc. 30% of a syringe is measured as so many mL. The 0.9 solution or NS is so many mg or grams of NaCl in water, and 1/2 NS is 1/2 that many grams or mg of NaCl in water, so you need to use those units of measure not %. Does this make sense?:)

Also on this site http://www.alysion.org/dimensional/analysis.htm#guide it says that you must first take a % and make it into a workable math term ie; such as a decimal which is what I was trying to accomplish by doing the problem with ....

.5 x .9g

-------

100g solution

I didn't label it as precisely as I should have but my percentage was taken care of and accounted for in my solution

I see, but are you sure it's .5 for 1/2 NS? On IV bags it says .45% for 1/2 NS. Is that what the site says? It would be 50% of the original amount, but .45% of solution. I was taking amount in the original problem to mean amount of NaCl added to make that concentration. But maybe they just mean amount as total percent of the solution is NaCl? I hate when words don't mean what I think they mean, lol!

I see, but are you sure it's .5 for 1/2 NS? On IV bags it says .45% for 1/2 NS. Is that what the site says? It would be 50% of the original amount, but .45% of solution. I was taking amount in the original problem to mean amount of NaCl added to make that concentration. But maybe they just mean amount as total percent of the solution is NaCl? I hate when words don't mean what I think they mean, lol!

Well the 0.5 is only part of coming to the .45%....0.9% also has to be considered which is where the .45% comes from....multiplying the two values 0.5 X 0.9= .45%............And the way they tell you to solve for the problem using the formula method is using the percent x the volume divided by 100 to come to the total......here is a link to the page where they do it that way http://www.dosagehelp.com/iv_amount.html This is how I initially knew that the percentage had to come into play.....it was just figuring out how to do the whole thing in DA that was baffling me..........I have since done a bunch of the problems, using the DA formula I came to a few posts back and they all have come out correct so I MUST be doing it right.

Not sure if any of the links I posted will be helpful to you or hindering if they are too different from how you're being taught..........they have been a very valuable resource for me and unlimited problems to practice, which is very nice.

Hope they make some sense to you :)

Hello everyone this is my 1st post and not really sure if I'm posting this in the correct place, but here goes...

Question 1:

Order: Nitroglycerin 0.4 mg sublingual every 5 minutes x3 as needed for chest pain. Pharmacy sends you Nitroglycerin 400mcg tablets. How many tablets will you adminster?

Question 2:

Order: Tetracycline 250mg orally 4 times a day for infection. Pharmacy sends you Tetracycline 500mg tablets. How many tablets do you adminster in a dose?

O.K. First off in question 1 I know the conversion of 0.4mg=400mcg=1 tab...but the x3 and the lack of "in a dose" confuses me into thinking the answer is 3...which my professor says is 1!!!

Obviously question 2 is 0.5 tablets in a dose...Am I crazy or is part of the question missing??

thanks anyone can PM me my test is on Tuesday...