Free PTCB practice quiz 5 # 4

by Judy Lav

Would you please show me how to arrive at this answer? I thought I was getting a handle on alligations, but this one throws me because I do not see enough information to fill in the-tic-tac-toe grid as far as my understanding of it is.

You have been asked by the Pharmacist to prepare 3 liters of a 30% strength solution. Your pharmacy stocks the active ingredient in 8 oz bottles of 70% strength. How many bottles of the active ingredient will you need to open to complete this request?
A 14
B 10
C 6
E 3

Thank you so much

Reply (Keith): Hi Judy, Indeed, this question was written (on purpose) in a way which throws many people off. However, I wrote it that way because I feel that it helps people to better develop test taking muscles. After reading the question, you are probably asking: "but what are we mixing it with?"

So, when you aren't given another(lower)strength to mix with, then you must default to using Water or NS or something with 0% of the active ingredient. Therefore, that is what you put in the other spot in the tic-tac-toe 0

Here it is step-by-step

On the exam, you must be prepared for these types of questions. They are testing to see what you know, sure... but also how well you can "Think on your feet", which is equally important.

Comments for
Free PTCB practice quiz 5 # 4

Click here to add your own comments

Quiz 5 Problem 4
by: Anonymous

I wonder if this is also a way to solve?

30% is 30g/100ml
3L =3000ml so you need (30g * 3000) / 100 = 900g
70% is 70g/100ml and 8oz. bottle is 250ml,
so (250*70g)/100 = 175g.
you need 900g/175g= 5.1 or 6 bottles.

Reply (Keith): Yes, looks good. There are at least 4 ways to solve it. It really depends on the person and what kind of math they are comfortable with / good at. Thanks for your comment and help.

Can I solve by this way?

Can I solve this way?
C1 x V1=C2 x V2
70 x V1=30 x 3000mL
V1=30 x 3000mL / 70
=1286mL =43 oz
1botlle/8 oz
?botlle/43 oz
X = 5,375
= 6 bottles

Click here to add your own comments

Join in and write your own page! It's easy to do. How?
Simply click here to return to Pharmacy math questions