Question

You need to prepare 50g of an ointment with 15% of zinc oxide. However, your pharmacy has no zinc oxide powder (how????) and the only thing you have is two lots of zinc oxide ointment containing, respectively, 50% and 5% of zinc oxide. How many grams of the 50% ointment you need to prepare this formula?

I know the correct answer is 11.11g but how do we get the answer

Can you please explain step by step on how to get the answer?

Answer 1

This will be solved using Alligation. Using the following formula for mixtures:

where

--------------(mass conservation law)

here for this question,

mf= mass of 15% zinc oxide = 50 g

m1= mass of 50% zinc oxide = x g

m2= mass of 5% zinc oxide = mf - m1= (50 - x) g

Also,

cf= 15%

c1= 50%

c2= 5%

(The concentrations of the zinc oxides)

Thus the equation will be:

Thus the amount of 50% zinc oxide required will be 11.11 grams.

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