Order of Operations (PEMDAS)

Why This Matters for Nursing: When calculating medication doses, you often have multiple steps. Doing operations in the wrong order gives wrong answers—and in healthcare, wrong answers can be dangerous.

What You Need to Know

PEMDAS tells you the order to perform mathematical operations:

Important Rules:

• M and D are equal — do them left to right
• A and S are equal — do them left to right
• Work from innermost parentheses out

🧠 Memory Trick

"Please Excuse My Dear Aunt Sally"

P - Parentheses first E - Exponents next M/D - Multiply or Divide (left to right) A/S - Add or Subtract (left to right)

Step-by-Step Process

Example: Solve 3 + 4 × 2

❌ Wrong: 3 + 4 = 7, then 7 × 2 = 14

✅ Right: 4 × 2 = 8 first (M before A), then 3 + 8 = 11

✏️ Worked Examples

Example 1: Basic PEMDAS

Problem: 10 - 3 × 2 + 4

Step 1 — Scan the expression for the highest-priority operations. There's a multiplication (3 × 2). No parentheses or exponents. Multiplication goes before addition/subtraction.

Step 2 — Do the multiplication first. 3 × 2 = 6. Rewrite the expression: 10 - 6 + 4.

Step 3 — Now handle addition and subtraction left to right. Left to right means we do 10 - 6 first (it's on the left): 10 - 6 = 4. Then 4 + 4 = 8.

Answer: 8