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Pharmacy Mixture Calculations

by Andrea

30 grams of hydrocortisone 2.5% ointment is combined with 15 grams of hydrocortisone 1% ointment. What is the percentage of hydrocortisone in the final product?

Comments for Pharmacy Mixture Calculations

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how to solve
by: Brad Wojcik, Pharm D

You have to know how many grams of HC and the total weight of the final product to calculate the final concentration. You have 30 g of 2.5% oint and 15 g of 1 % oint. You know you will end up with 45 g of final product by adding the 30 g and 15 g, that part is easy. In the 30 g of 2.5% you have 0.75g 30g oint(2.5g HC/100 g oint)= 0.75g and you have 0.15 g in the 15 g for a total of 0.9g HC. You end up with 0.9g HC/45 g oint, now change to a % by multiplying by 100%
(0.9g HC/45g oint)(100%) = 2% w/w
And yes, you multiply by 100%, not 100.

unknown numbers
by: Anonymous

How did you get 0.75?

by: Anonymous

the 0.75 is the result of the (2.5/100)

How did you get 0.15g?
by: Anonymous

How did you get 0.15g?

Thats what I got
by: Anonymous

0.15 came from:
You have (15) grams of 1%

1%= 1/100
= 0.01
= (15)*0.01
= 0.15

I Found it simpler to just do it like this
by: Anonymous

[30g(2.5%)] + [15g(1%)] = 45g(x%)

(75g%) + (15g%) = 45g(x%)

90g% = 45g(x%)

90g% = 45g(x%)
---- ---
45g 45g

2% = x%

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