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percentage ratio math problems

by Marilyn

I keep getting stuck on problems that have the given % strength in a given volume. They then ask how many mg of active ingredient is in a desired dose. I keep getting these wrong, I am obviously doing something wrong. How do you solve these type of questions?

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Percentage problems
by: Brad Wojcik, Pharm D

These problems can be a little tricky. The first thing you have to do is determine if it % w/v, %v/v or % w/w. a 5% NaCl solution would be w/v because you weigh out the NaCl and measure the volume of the water. You can substitute g for w and mL for v. A 5% NaCl solution would then be 5% g/mL. You can get rid of the % sign by dividing by 100%. This gives you 5g/100 mL. Now you have a ratio which is easier to work with and can change it around to mg/mL, etc.

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