M3 · Ratios & Proportions

Every dosage calculation is a proportion. A stock label gives you one ratio; the ordered dose and the quantity to give are the other. This module names that structure and connects it to the dimensional analysis method you built in M2.

---

Learning Objectives

By the end of this module you should be able to:

• Write a medication ratio in fraction format
• Find a unit rate from a stock label
• Recognize when two ratios are equivalent
• Set up a dosage problem as a DA chain using the stock ratio
• Apply a reasonableness check to any calculated dose

---

Pages

• Ratios
• Proportions

---

Estimated Time

Approximately 1–1.5 hours including practice problems.

Before you begin

This module applies the DA skills from M2 directly to dosage problems. If unit cancellation feels shaky, do a quick review of Checking Your Setup before continuing.

Cross-multiplication

If you have learned cross-multiplication or ratio-proportion algebraic methods, those are covered in Additional Methods. They are not required if you are using dimensional analysis.