1. Review fractions, decimals, and percents
Ratios & Proportions
Ratios & Proportions
Before viewing this tutorial, you must have knowledge of fractions, decimals and percents. Click the link at the bottom of the screen for a review or click the arrow to advance to the next screen.
Pima Medical Institute Online
Review fractions, decimals, and percents

2. A ratio is a way of showing the relationship between two numbers
Ratios
A ratio is a way of showing the relationship between two numbers
1 tablet : 100 mg
100 mg : 1 tablet
Written with a colon
Written as a fraction
1 tablet
250 mg
1mL
50 mg
A ratio is a way of showing the relationship between two numbers. A ratio can be written with a colon. Here’s an example that you might find in pharmacology. 1 tablet : 100 mg or 100 mg : 1 tablet
Ratios can also look like fractions. Here’s another example that you might find in pharmacology: 1 tablet / 250 mg.
Here’s another example using liquid measurements: 1/50 means that 1 mL contains 50 mg.

3. If 1 tablet contains 100 mg, then 2 tablets contain 200 mg
Proportions
A proportion is a way of showing the relationship between two ratios
1 tablet : 100 mg = 2 tablets : 200 mg
If 1 tablet contains 100 mg, then 2 tablets contain 200 mg
1 tablet
100 mg
2 tablets
200 mg
A proportion shows the relationship between two ratios. If 1 tablet contains 100 mg, then 2 tablets contain 200 mg. The proportion would look like this.
1 tablet : 100 mg = 2 tablets : 200 mg
1 tablet / 100 mg = 2 tablets / 200 mg
Remember that one side of the equation must equal the other side.
One side of the equation must equal the other side

4. Solve for an unknown (n)
If 1 tablet contains 100 mg,
how many milligrams do 4 tablets contain?
If 3 values are supplied in a proportion statement, you can solve for
the 4th value
1 tablet
100 mg
4 tablets
n mg
Unknown value
(1 tablet)(n mg)
(4 tablets)(100 mg)
If 3 values are supplied in a proportion statement, you can then use the relationship to solve for the fourth value.
For example, if 1 tablet contains 100 mg, how many milligrams do 4 tablets contain?
First, identify the ratios.
1 tablet / 100 mg
4 tablets / n mg  Contains unknown value
Then put an equals sign between them to set up the proportion statement.
Now to solve for n, you cross multiply. Recall that when a unit or number is in both the numerator and denominator, you can cancel them out.
This gives us n = 400. Our answer is 4 tablets contain 400 mg.
Identify the ratios.
Put an equals sign between.
Cross multiply. n
(4 tablets) (100mg)
1 tablet n
400 mg

5. Self Test: Ratio and Proportion
Now, try it on your own.

6. Presented by PMI Online Education
Resources:
Essential Calculations for Veterinary Nurses and Technicians by Terry Lake and Nicola Green
Applied Pharmacology for Veterinary Technicians, 4th Edition by Boyce P. Wanabaker and Kathy Lockett Massey