How to Calculate Percentages
A percentage is a way of expressing a number as a fraction of 100. The word "percent" literally means "per hundred." Understanding percentages is essential for everyday tasks like calculating tips, discounts, tax, and interest rates.
Common Percentage Formulas
1. Finding a Percentage of a Number
Result = (Percentage / 100) × NumberExample: What is 15% of 200? → (15/100) × 200 = 30
2. Finding What Percentage One Number Is of Another
Percentage = (Part / Whole) × 100Example: 30 is what percent of 200? → (30/200) × 100 = 15%
3. Percentage Change (Increase or Decrease)
Change = ((New - Old) / Old) × 100Example: From 80 to 100 → ((100-80)/80) × 100 = 25% increase
Practical Uses of Percentages
- Shopping: Calculating discounts (20% off a $50 item = $10 savings)
- Tipping: Calculating restaurant tips (15-20% of the bill)
- Finance: Understanding interest rates, investment returns, and inflation
- Grades: Converting scores to percentages (45 out of 50 = 90%)
- Cooking: Scaling recipes up or down by a percentage
Frequently Asked Questions
How do you calculate a percentage?
To calculate a percentage, divide the part by the whole and multiply by 100. For example, if you scored 42 out of 50 on a test: (42 / 50) × 100 = 84%.
How do you find the original number from a percentage?
If you know that a number is a certain percentage of the original, divide the number by the percentage (as a decimal). For example, if 30 is 15% of the original: 30 / 0.15 = 200.