Alligation question from Canada


(Canada)

How many grams of sulfathiazole should be added to
3400 g of a 10% sulfathiazole cream to prepare a cream containing 15% sulfathiazole? The answer key says 200 g and I've tried it every way I can think of and cannot get this answer of 200 g.

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Reply
(by Keith)

An Alligation can work like this:

1) Play some tic-tac-toe


100 - -   - 5 parts
- - - 15 -
10 - - - - 85 parts


2)Reduce your parts to:

1 part (100%) to 17 parts (10%)


3)Divide your initial volume (10%) by it's # of parts.

3400 ÷ 17 = 200


4)Multiply that amt by the other strengths # of parts.

200 X 1 = 200


But... I'm actually a bigger fan of using an
algebra equation:


3400(.10)+(X)(1.0)=(3400+X)(.15)

340 + X = 510 + .15X

.85X = 170

X = 200

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