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Old 21-07-2009, 09:03 PM   #1
Day Tripper
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Help for lame stuff?

Word problems...

I could do these not too long ago but my brain has recently lost the ability. I'm trying to study for my National Certification or whatever.

If a physician orders 25% dextrose 1000 ml and all you have is 70% dextrose 1000 ml, how much 70% dextrose and how much sterile water will be used?

If 200 grams of dextrose is ordered using a 50% dextrose solution, how many ml are needed?

How much talc is needed for an order for 120 gm of the following compound:
nupercainal ointment 4%, zinc oxide 20%, talc 2%?


I know the exam is multiple choice but these questions come in the practice exams I have. I need to know how to do them and be able to understand them for that purpose. The books I have to reference aren't too clear and do not explain these sorts of things too well.

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Old 21-07-2009, 09:08 PM   #2
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Old 21-07-2009, 09:32 PM   #3
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Well for the first one, a 25% dextrose solution of 1000 ml is really 250 ml pure dextrose per 1000 ml. A 70% solution means you need more than 250 ml of it. Since it's multiple choice, I'd just use that to rule out a couple answers, and then plug in the logical ones to see which one fits.

Not sure about converting grams and ml in the 2nd one.

For the 3rd,
120 gm x .02 = 2.4 gm talc. I think that'd be right.


Last edited by Tuesday : 21-07-2009 at 10:09 PM.
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Old 21-07-2009, 09:43 PM   #4
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Quote:
Originally Posted by Something Vague View Post
ok is the first one 357ml dextrose 643ml water. i tried in my head to figure it out and it hurt haha.
347 dextrose : 643 water would be approx. a 46% dextrose solution.

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Old 21-07-2009, 09:52 PM   #5
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Quote:
Originally Posted by Something Vague View Post
aw why isn't my brain logical :(

i tried to figure the first one out like this;

500ml of 70% solution + 500ml water = 1000ml 35% solution. so then 50ml = 3.5%. 3.5% into 25% = 7.1. 7.1 x 50ml = 357.

so 357ml of 70% dextrose and 643ml water.

i failed maths?
Ok, I think the bolded part is right so far. But then 50 ml is one fifth of the 1000 ml, so dividing 35% by 5 = 7% ...hovever now I am thoroughly confused :P I'm not the best at maths either.

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Old 21-07-2009, 09:55 PM   #6
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Ok, after re-doing this about 12 times, I think you were right. So sorry! :P I'm an idiot haha.

Sorry I'm totally spamming this thread :P


Last edited by Tuesday : 21-07-2009 at 10:12 PM.
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Old 21-07-2009, 09:56 PM   #7
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Ok i can do maths but that blows my brain to pieces is there an easier question? :p

Hope it goes well tho Shan




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Old 21-07-2009, 10:02 PM   #8
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ok... I'm a physiology student and my boyfriend is a pharmacology student and neither of us can remember how to do this... lol, not good with exams being only 3 weeks away...



I'll come back when my memory decides to function

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Old 22-07-2009, 11:42 AM   #9
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Quote:
Originally Posted by Day Tripper View Post
If a physician orders 25% dextrose 1000 ml and all you have is 70% dextrose 1000 ml, how much 70% dextrose and how much sterile water will be used?
wouldnt it be something along the lines of (25/100)X 70 = 17.5 (17.5 X 1000)=17500 so it would be 1000ml of dextrose an 7400 of water. but that seems well out.




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Old 22-07-2009, 12:01 PM   #10
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I think my brain jus exploded... Very messy...


Good luck!



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Old 22-07-2009, 12:04 PM   #11
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I am currently hunting for the lecture notes from when I learnt how to do these calculations...


hopefully will return soon with knowledge lol

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Old 22-07-2009, 01:20 PM   #12
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Originally Posted by Scarletts Web View Post
well that is incredibly hard, i tried and failed miserably to work it out.



We are not our failures...


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Old 22-07-2009, 05:27 PM   #13
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I assume you cant purify the 70% dextrose into solid form and then make it that way?
Quote:
Originally Posted by Day Tripper View Post
If a physician orders 25% dextrose 1000 ml and all you have is 70% dextrose 1000 ml, how much 70% dextrose and how much sterile water will be used?
700/1000 dextrose and 300/1000 water, So you need to make the 700 = 25%. So then the total must be 700*4= 2800 so you need to add 1800ml of water. When then it'll be 700ml of dextrose and 2100ml of water. And then you can take 1000ml from this and have 1800ml left over? Is that cheating?

Rest are bla.

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Old 22-07-2009, 05:32 PM   #14
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gah! this is starting to frustrate me lol


almost tempted to email my tutor and ask how to do it

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Old 22-07-2009, 05:55 PM   #15
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ok... I think I've found the right set of lecture notes... I've found these 2 examples so far of similar types of calculation... my maths fails, but I thought I'd put them up in case they help anyone work anythi gout...

I'll keep looking for the exact manor for doing this


Quote:
General formula for solving: Amt1 x %1 = Amt2 x %2
Amt1 = the quantity or amount of the ORIGINAL preparation.
%1 = the % strength of the ORIGINAL preparation expressed as a decimal or percent
Amt2 = the quantity or amount of the WANTED preparation
%2 = the % strength of the WANTED preparation expressed as a decimal or percent
To solve concentration and dilution problems you need to identify the two preparations in the equation, convert ratio or percentage strengths to decimal expressions and convert to same systems of measurement.

EXAMPLE: If 500 ml of a 15% solution are diluted to 1500 ml, what will be the percent strength?

Amt1 x %1 = Amt2 x %2
Step 1: Identify the two preparations in the problem and assign values to appropriate terms.
Step 2: Solve the equation by multiplying and solving for X.
500 ml x 15% = 1500 ml x X%
7500 = 1500X
7500/1500 = 1500X/1500
X = 5%
Quote:
If 8 ml of phenol were added to 480 ml of lotion, what is the percentage of phenol in the lotion?
8 ml (Active Ingredient)

(Total Amt) 480 ml X %
Divide to solve for X.
8 / 480 = X

EXAMPLE: If 1.2 gm of menthol is added to 480 ml of lotion, what is the percentage of menthol in the lotion?

1.2 gm (Active Ingredient)
(Total Amt) 480 ml X %
Divide to solve for X.
1.2 / 480 = x
x = 0.0025

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