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What is a Percentage?

A percentage is a number expressed as a fraction of 100. The word comes from Latin "per centum" meaning "by the hundred." It's one of the most useful mathematical concepts in daily life.

Basic Percentage Formula

Percentage = (Part / Whole) x 100

Example: What percentage is 25 out of 200?

(25 / 200) x 100 = 12.5%

Three Common Percentage Questions

1. What is X% of Y? -> (X/100) x Y

2. X is what percent of Y? -> (X/Y) x 100

3. X is Y% of what number? -> X / (Y/100)

Quick Mental Math Tricks

Finding 10%: Move the decimal one place left

10% of $85 = $8.50

Finding 5%: Find 10%, then halve it

5% of $85 = $8.50 / 2 = $4.25

Finding 15%: Find 10% + 5%

15% of $85 = $8.50 + $4.25 = $12.75

Finding 20%: Find 10% and double it

20% of $85 = $8.50 x 2 = $17.00

Finding 25%: Divide by 4

25% of $85 = $85 / 4 = $21.25

Percentage Increase/Decrease

Percentage Change = ((New - Old) / Old) x 100

Price went from $50 to $65: ((65-50)/50) x 100 = 30% increase

Price went from $80 to $60: ((60-80)/80) x 100 = -25% decrease

Common Uses of Percentages

Discounts and sales (20% off)

Tips (15-20% at restaurants)

Tax rates (income tax, sales tax)

Interest rates (savings, loans)

Grade scores (85% on a test)

Statistics and data analysis

Use Our Percentage Calculator

Try our free percentage calculator to solve any percentage problem instantly.