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Quick Calculations
How to Calculate Percentages
0% of 100 = 0.00
To find X% of a number Y, multiply Y by X/100. This is useful for calculating discounts, tips, tax amounts, and proportions.
Step-by-Step
- Take the percentage: 0%
- Divide by 100: 0 ÷ 100 = 0
- Multiply by the number: 0 × 100 = 0.00
Formula: result = number × (percentage ÷ 100)
💡 Mental Math: 10% = move decimal left 1 place. 1% = move decimal left 2 places. 50% = divide by 2. 25% = divide by 4.
Common Percentage Calculations
| Calculation | Result |
|---|---|
| 10% of 100 | 10 |
| 15% of 200 | 30 |
| 20% of 50 | 10 |
| 25% of 80 | 20 |
| 8% of 1,000 | 80 |
| 12% of 500 | 60 |
Understanding Percentages
What is a Percentage?
A percentage (%) means "per hundred." 15% = 15/100 = 0.15. Percentages express ratios as fractions of 100 and are used in discounts, interest rates, statistics, and everyday calculations.
Common Uses
- Discounts: "30% off" means multiply price by 0.70
- Tips: 15-20% of bill total
- Interest: APR expressed as yearly percentage
- Statistics: "45% of users prefer X"
- Grades: Test scores as percentages
Percentage Point vs Percent Change
Moving from 10% to 15% is 5 percentage points, but it's a 50% increase (15/10 - 1 = 0.5). Don't confuse these when discussing changes.
Quick Reference
- 10% = 0.10 = 1/10
- 25% = 0.25 = 1/4
- 50% = 0.50 = 1/2
- 75% = 0.75 = 3/4
- 100% = 1.00 = whole
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Frequently Asked Questions
Multiply the number by the percentage (as decimal). Example: 20% of 150 = 150 × 0.20 = 30.
X% of Y = Y × (X ÷ 100)
X is what % of Y = (X ÷ Y) × 100
% increase = ((new - old) ÷ old) × 100. From 50 to 75: ((75-50) ÷ 50) × 100 = 50% increase.
If something is 20% off and costs $80, original price = 80 ÷ 0.80 = $100. Divide by (1 - discount% as decimal).
15% of 200 = 30. (200 × 0.15 = 30)