## Ointment Strength Calculation

by Tyson

I'm preparing for a PEBC EVALUATION exam and I'm stumped on this question. Several pharmacists and technicians have come up with the answer of 4.8g, however, the answer presented in the seminar indicates the answer to be 6g. Which answer is correct?

The question is :
How many grams of HC powder should be added to 32g of 5% HC oint to prepare an oint containing 20% of HC.

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## Comments for Ointment Strength Calculation

 Mar 15, 2012 the answer by: Anonymous the answer is 4.8g, there are 1.6g of HC in the 32g 5% ointment, and there are 6.4g in a 32g 20% ointment,so all you have to do is (6.4g-1.6g= 4.8g)

 Sep 06, 2011 Easy Way to Allligate!!! by: ChRxis The answer is 6gm-100- - - - 15 - - - -20 -5- - - - - 80-Standard alligation, although you have no final amount. So in this case, all you need to do now is set up a proportion:20 = x80 15if you consider the fact that 80 is representative of the 5% cream. 20 gm of the 5% cream is 80% of the entire amount. Therefore 6gm of HC powder is equal to the remainder.

 Aug 31, 2011 quantity x strength solution by: Anonymous The solution:have/quantity x strength = need/quantity x strength. have need 32g (5%) = ?g (20%)divide by 20% on both sides have need 32g (5%)/20% = ?g (20%)/20% (cancels out)32 x 5 = 160160 / 5 = 8gAnswer: 8 grams of HC

 Aug 23, 2011 6 grams by: MTL Determine HC powder is a 100% solutionLet x = grams of HC powderThen:100% of how much HC powder when added to 32 grams of 5% powder will make the 32 grams you have plus the grams you'll have to add of 20% ointment.Mathematically it looks like this:1x + 32*0.05 = (32 + x)*.21x + 1.6 = 6.4 + 0.2x0.8x + 1.6 = 6.40.8x = 4.8x = 6This is straight Algebra and may be confusing to you, as I don't know what an alligation table is. If this doesn't make sense to you sorry if I confused you more.

 Aug 17, 2011 ? by: Anonymous 32 grams * 5% = 20% * x x= unknown amount 160 = 20% * x 160/20= x x= 8 grams

 Aug 16, 2011 previous problem by: Anonymous oops I spelled alligation incorrectly. sorry

 Aug 15, 2011 Same method for this problem? by: Anonymous That's good you posted another response. Earlier today I was trying to figure out why I couldn't get the same answer you got from the allegation table I made. Can we use that same allegation method to solve this problem?How much 75% ethanol is needed to make 300ml of 30% ethanol?A. 80mLB. 120mLC. 180mLD. 240mL

 Aug 15, 2011 Tricky prob ..we need help pls by: Kim I realize that I made a mistake working this problem (when I wrote it down). I used 50% instead of 5% . Don't want it to go without notice and confuse anyone.I came up with 4.6 grams for final answer. Tough one)

 Aug 12, 2011 My answer is 6 grams. by: Kim Use the standard alligation tic-tac-toe setup. Since you are not given the strength of the HC powder, make it 0% in the alligation. 50% 20% 2/5=.4 x 32g = 12.8 (13) 20% 0% 30% 3/5=.6 x 32g = 19.2 (19) 19 - 13 = 6g Hope this helps.

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