Calculating Percentages Quiz

Calculating Percentages

• Definition: A percentage represents a fraction out of 100. It is often used to express how much of something exists relative to a whole.

• Basic Formula:

  • Percentage (%) = (Part / Whole) × 100

• Finding a Percentage of a Number:

  • Example: To find 20% of 50:
    • Calculation: 20% of 50 = (20/100) × 50 = 10

• Finding What Percentage One Number Is of Another:

  • Example: To find what percentage 25 is of 200:
    • Calculation: (25 / 200) × 100 = 12.5%

• Increasing a Number by a Percentage:

  • Example: Increase 100 by 15%.
    • Calculation: 100 + (15/100) × 100 = 115

• Decreasing a Number by a Percentage:

  • Example: Decrease 80 by 25%.
    • Calculation: 80 - (25/100) × 80 = 60

• Converting Fractions to Percentages:

  • Multiply the fraction by 100.
  • Example: (3/4) × 100 = 75%

• Converting Decimals to Percentages:

  • Multiply the decimal by 100.
  • Example: 0.85 × 100 = 85%

• Percentage Increase/Decrease Formula:

  • Percentage Increase = [(New Value - Original Value) / Original Value] × 100
  • Percentage Decrease = [(Original Value - New Value) / Original Value] × 100

• Common Percentage Values:

  • 10% = 1/10
  • 20% = 1/5
  • 25% = 1/4
  • 50% = 1/2
  • 75% = 3/4

• Tips for Quick Calculations:

  • 1% of a number: Divide by 100.
  • 10% of a number: Divide by 10.
  • 50% of a number: Divide by 2.
  • 25% of a number: Divide by 4.

Understanding Percentages

• A percentage is a way to express a part of a whole, represented as a fraction out of 100.
• The basic formula to calculate percentage is:
• Percentage (%) = (Part / Whole) × 100*

Calculating Percentages of Numbers

• To find a specific percentage of a number, apply the formula:
  For example, to determine 20% of 50:
  (20/100) × 50 = 10

Determining Percentages Between Numbers

• To find what percentage one number is of another:
  Example: 25 is what percentage of 200?
  Calculation: (25 / 200) × 100 = 12.5%

Increasing and Decreasing Values by Percentages

• To increase a number by a percentage:
  For example, to increase 100 by 15:
  Calculation: 100 + (15/100) × 100 = 115
• To decrease a number by a percentage:
  Example: Decrease 80 by 25%:
  Calculation: 80 - (25/100) × 80 = 60

Converting to Percentages

• Fractions to Percentages: Multiply the fraction by 100.
  Example: (3/4) × 100 = 75%
• Decimals to Percentages: Multiply the decimal by 100.
  Example: 0.85 × 100 = 85%

Percentage Change Calculations

• Percentage Increase:
  Formula: [(New Value - Original Value) / Original Value] × 100
• Percentage Decrease:
  Formula: [(Original Value - New Value) / Original Value] × 100

Common Percentage Equivalents

• 10% = 1/10
• 20% = 1/5
• 25% = 1/4
• 50% = 1/2
• 75% = 3/4

Quick Calculation Tips

• For fast percentage calculations:
  • 1% of a number: Divide the number by 100
  • 10% of a number: Divide the number by 10
  • 50% of a number: Divide the number by 2
  • 25% of a number: Divide the number by 4