# Compounding Quantity Needed

by Amber
(Austin)

A custom preparation batch calls for a several liters of 8% alcohol solution. The pharmacy manager has asked you to check and calculate how much 8% can be compounded with stock on hand. You only find 1500mL bottle of 20% alcohol solution. What quantity will you report?

A. 4250 mL
B. 4500 mL
C. 3750 mL
D. 2250 mL

### Comments for Compounding Quantity Needed

 Use Algebra on this one by: Jerry 1) What are your factors: What you have - - = - - What you want (1500mL of 20%) - = - - (How many mL of 8%) 2) This is an equation calculation: (1500mL)(20%) = (X mL)(8%) 3) Simplify the terms and do the Algebra: (1500)(0.20) = (X)(0.08) 4) Keep breaking down to isolate X 300 = 0.08X 5) Solve for X 300 - - 0.08X ---- = ------- 0.08 - - 0.08 6) X = 3750 - An alligation could be used on this one also, but this Algebra is quicker and cleaner for this scenario.

 Pharmacy Tech for 4 yrs. by: Kristina M. I really like your explanation a lot sir. This is make everybody understanding very well. Thank you very much for showing the math.

 nice by: Anonymous the best explanation for this question. simple and straight to the point.

 Compounding Quantity by: Anonymous Easier way is to use ratios. 20% is 2.5times greater than 8% (just do 20/8) and then multiply the total volume (1500) by 2.5 = 3750mlEXL 20/8= 2.5 x 1500 = 3750ml

 very nice explanaions by: Anonymous I really like both explanations, but the second one is the easiest one for me. Thank you very much for explaining

 easy by: Anonymous 20%/8% *1500=3750

 Alligations vs. V1 x C1 = V2 x C2 by: Anonymous I was taught to use alligations to solve problems like this, how come if you use alligations you don't come up with the same answer?

 Doing with Alligation by: Jerry Attn: AnonymousIf you get a different calculation using alligation, it means you're doing the alligation wrong.20% | - | 8 Parts ------------------- - | 8%| - - ------------------- 0% | - | 12 Parts------- = 20 Parts total And so,- If 8 of the parts = 1500mL, then what volume is 20 parts?1500mL - - X ------- = -------8 part - 20 partDoes this help? Maybe your syntax was off a little?

 THANK YOU GUYS by: Anonymous Thank you very much for the amazing explanation really kind of hard question... appreciate it

 great by: Anonymous its easy to understand the explanation. thank u for showing how to get the answer.

 ThankYou by: Joni For some reason, I get stumped on these questions. I got the right answer in a round-a-bout way but explanation one was much more concise.

 thank you! by: manda thank you! that was very helpful!