4B Percent of a Number Study Guide

Key Vocabulary

Percent of — a part of a number found by multiplying. The word "of" means multiply. (porcentaje de)

Base — the whole number you are finding a percent of. (base)

Part — the answer you get when you find a percent of a number. (parte)

Whole — the total amount; the number that represents 100%. (entero / total)

"Of" means multiply — when you see "percent OF a number," it tells you to multiply.

Visual Example

Think of "percent of" as cutting a piece from the whole:

25% of 80 = ?

Imagine 80 split into 4 equal parts (because 25% = 1/4):
[20] [20] [20] [20]

One part = 20
So 25% of 80 = 20

Step-by-Step

1 Convert the percent to a decimal (divide by 100).
2 Multiply the decimal by the number (the whole).
3 The result is the part.

Example: Find 30% of 200
Step 1: 30% = 30 ÷ 100 = 0.30
Step 2: 0.30 × 200 = 60
Answer: 30% of 200 = 60

Example: Find 150% of 40
Step 1: 150% = 150 ÷ 100 = 1.50
Step 2: 1.50 × 40 = 60
Answer: 150% of 40 = 60 (more than the original because it’s over 100%)

Formula Box

Part = Percent (as decimal) × Whole

Remember: "OF" = multiply | "IS" = equals

Watch Out!

Convert the percent FIRST! 25% of 80 is NOT 25 × 80 = 2000. You must change 25% to 0.25 first.
Percent over 100% gives a number BIGGER than the whole. 150% of 60 = 90 (bigger than 60).
"Of" always means multiply in percent problems.

Practice Problems

1. Find 20% of 150.

2. Find 75% of 200.

3. Find 8% of 50.