Percentages Ratios and Proportions
Ratio = the relation between two similar magnitudes with respect to the number of times the first contains the second: the ratio of 7 to 2, written 7:2 or 7/2.
Proportion = comparative relation between things or magnitudes as to size, quantity, number, or ratio: 7/2 = 14/4
Percentage = a rate or proportion per hundred: 7/2 = 350%
Example:
If 5 tablets of Lipitor contain 20 grams of Lipitor, how many tablets are required to fill a prescription for 500 grams?
20 grams / 5 tablets = 500 grams / X tablets
4 grams / tablet = 500 grams / X tablets
X = 500 / 4
125 tablets
How many ml of solution containing 150 mcg of medication per ml must be administered to a patient that requires 1 milligram?
150 mcg / mL = 1 mg / X mL
150 mcg / mL = 1000 mcg / X mL (converted from mg to mcg)
X mL = 1000 / 150
X = 6.67 mL
How many grams of medication are required to make 100 mL of 1:5000 solution?
1 gram / 5000 mL = x grams / 100 mL
100 * (1/5000) = x grams
x = 0.02 grams