Help with this PTCB question

[steveysmith54]

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If a tech uses 350mg in D5W 500cc prepared with 500mg/20cc stock. How much stock injuection is added to create d5w.

this is exactly how the question is pharased, i am really struggling w/ it.

 

[dragonqueen209]

is the answer 14 cc?

 

[steveysmith54]

yeah it is.... how do u get this. i already took my ptcb today, so it's kinda late.

 

[steveysmith54]

I think i had similar questions, i just used kinda my insticts to ignore tge d5w and 500cc to just try to find what volume of stock u need to get to 350 mg.

i never really understood this question.

 

[lostuc]

i think its what u want divided by what u have x's the avaiable amount so in this case 350/500 x 20.

 

[steveysmith54]

i think its what u want divided by what u have x's the avaiable amount so in this case 350/500 x 20.

oh right u ignore the d5, but u just don't need the entire 500mg/20cc stock, u need part of it..... oh ok

 

[sdn1977]

I gotta wonder what is the purpose of a question like this? I mean really - who would come up with such a weird question????

If I wanted the tech to be able to draw up 350mg of dextrose from a set stock solution...that would be reasonable to ask (altho not very practical!) - perhaps a different drug than dextrose.......

However...I will caution you not to give out "remembered" questions. I think the confidence of the exam is something you sign when you take the exam - at least it is with the NABPLEX.

Try to change your question to something which is not so "exact".

 

[steveysmith54]

this question is actually from noeh ptcb review book.

not the exam... still wrong for me to do this.

there were at least two questions that had similar concept of not givign entire stock, but parts of it.

so learn it future test takers.

 

[steveysmith54]

also what really confused me is this question says " the tech uses . Sounds too me like the tech is trying to make this soln from stock. he is using the stock to make.

at first it sounds like it was a dilution problem.

 

[Farmercyst]

If a tech uses 350mg in D5W 500cc prepared with 500mg/20cc stock. How much stock injuection is added to create d5w.

this is exactly how the question is pharased, i am really struggling w/ it.

If he/she is making 0.7mg/mL from 25mg/mL and needs 350mL of the diluted solution then you have to use 0.7mg/mL* 350 mL = 245 mg
245 mg/25 mg/mL = 9.8 mL

Check the math, I didn't have a calculator. If I understand the question right, this should be the answer.