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Percentages (%)

Overview

Per 100.

What is it?

A fraction where the denominator is always 100.

History

Used by Roman Emperors to tax their citizens.

Key Idea

To get 10%, just move the decimal one spot left.

Practice This Topic

Concept Guide

Plain English: Percent literally means 'Per Cent' (for every 100). 50% means 50 for every 100. It's the universal language of discounts, batteries, and grades.

Real-world example: Battery life on your phone. Sales tax. Tips at a restaurant.

How to do it

  1. Convert % to decimal (move dot 2 left).
  2. Multiply by total.
  3. That is the 'part'.
  4. Add/Subtract from total if needed.
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Common Pitfall

Computing sales tax and forgetting to ADD it to the original price.

Word Problem
"A $50 hoodie is 20% off. How much do you save?"
Reasoning: 10% of 50 is 5. So 20% is 10. You save $10.

Practice Examples

The Tip
Bill: $40 10% = $4 20% = $8
Just double the 10%.