Here’s comprehensive content documentation for the percentage calculator code:

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Percentage Calculator Suite Documentation

1. Basic Percentage Calculator

Functionality: Calculate basic percentage relationships between three values:

• What is X% of Y?
• X is what% of Y?
• X is Y% of what?

Input Format:

[Percentage]% of [Number] = ?

Example:

25% of 200 = 50

2. Common Percentage Problems

a. X% of Y

Formula:
Result = (X/100) × Y

Example Calculation:

What is 15% of 200?
(15/100) × 200 = 30

b. X is what % of Y

Formula:
Percentage = (X/Y) × 100

Example Calculation:

25 is what % of 200?
(25/200) × 100 = 12.5%

c. X is Y% of what

Formula:
Original Number = X/(Y/100)

Example Calculation:

30 is 15% of what?
30/(15/100) = 200

3. Percentage Difference Calculator

Purpose: Compare two values and calculate their percentage difference

Formula:
Percentage Difference = (|V1 - V2| / ((V1 + V2)/2)) × 100

Example:

Value 1: 200
Value 2: 150
Difference = |200-150| / ((200+150)/2) × 100 = 28.57%

4. Percentage Change Calculator

Purpose: Calculate increase/decrease between old and new values

Formula:
Percentage Change = ((New - Old)/Old) × 100

Example:

Old Value: 200
New Value: 250
Change = ((250-200)/200) × 100 = 25% increase

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Key Features

1. Multi-Function Calculator

• 4 different percentage calculation modes
• Instant results with 2 decimal precision
• Clear input/output visualization

1. Input Validation

• Automatic number parsing
• Error handling for invalid inputs
• Zero-division protection

1. User Interface

• Responsive grid layout
• Color-coded sections
• Clear input labels
• Mobile-friendly design

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Usage Instructions

1. Basic Calculator

• Enter any two values
• Leave third field empty
• Click “Calculate”

1. Common Phrases

• Select problem type
• Fill known values
• Click corresponding calculate button

1. Difference Calculator

• Enter both values
• Click “Calculate Difference”

1. Change Calculator

• Enter old and new values
• Click “Calculate Change”

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Mathematical Formulas Used

1. Basic Percentage
   P% × X = Y
2. Percentage Difference
   (|A-B|/((A+B)/2)) × 100
3. Percentage Change
   ((B-A)/A) × 100

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Error Handling

1. Invalid Inputs

• Non-numeric values
• Empty required fields
• Negative percentages
• Error messages appear for:
  • Division by zero attempts
  • Missing required values
  • Invalid number formats

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FAQ Section

Q: How are decimal values handled?
A: All calculations support decimal inputs with automatic rounding to 2 decimal places.

Q: Can I calculate negative percentages?
A: Yes, but results will show appropriate positive/negative indicators.

Q: What if I get “Infinity” as result?
A: This indicates division by zero – check your input values.

Q: How precise are the calculations?
A: Calculations are precise to 2 decimal places for percentages and 4 places for raw numbers.

Q: What’s the difference between percentage difference and change?
A: Difference compares two values symmetrically, while change measures relative to original value.

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Development Notes

1. Technical Specifications

• Pure JavaScript implementation
• CSS Grid/Flexbox layout
• Mobile-first responsive design
• No external dependencies

1. Browser Support

• Chrome 50+
• Firefox 45+
• Safari 10+
• Edge 15+

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Sample Calculations

1. Discount Calculation

What is 30% of $150?
= (30/100) × 150 = $45 discount
Final price = $150 - $45 = $105

2. Grade Percentage

Scored 45/60 marks
Percentage = (45/60) × 100 = 75%

3. Population Growth

2010: 1,200,000
2020: 1,500,000
Growth = ((1.5M-1.2M)/1.2M) × 100 = 25% increase

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This documentation complements the calculator’s technical implementation by explaining its functionality, mathematical basis, and practical usage scenarios. The clean separation between different calculation types and intuitive UI make it suitable for both personal and educational use.he best way to achieve your goals.

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