Lecture on Fractions of Amounts

Introduction to Fractions:

• Understanding how to find a fraction of an amount.
• Key Concept: Divide by the denominator.

Common Fraction Calculations:

Half of a Number:

• Example:
  • Half of 20: 20 divided by 2 = 10.
  • Half of 14: 14 divided by 2 = 7.
  • Half of 60: 60 divided by 2 = 30.

A Third of a Number:

• Example:
  • Third of 15: 15 divided by 3 = 5.
  • Third of 30: 30 divided by 3 = 10.
  • Third of 18: 18 divided by 3 = 6.

A Quarter of a Number:

• Example:
  • Quarter of 100: 100 divided by 4 = 25. (Can use long division if needed)

A Fifth and a Tenth:

• Example:
  • Fifth of 35: 35 divided by 5 = 7.
  • Tenth of 80: 80 divided by 10 = 8.

Fractions with Numerators Greater Than One:

• General Rule: Divide by the bottom of the fraction (denominator) and multiply by the top (numerator).

Example Calculations:

• Two-Thirds of 15:

  • One third is 5 (15 divided by 3).
  • Two-thirds: 2 x 5 = 10.

• Three-Fifths of 20:

  • One-fifth is 4 (20 divided by 5).
  • Three-fifths: 3 x 4 = 12.

• Two-Ninths of 36:

  • One-ninth is 4 (36 divided by 9).
  • Two-ninths: 2 x 4 = 8.

• Two-Fifths of 600:

  • One-fifth is 120 (600 divided by 5).
  • Two-fifths: 2 x 120 = 240.

Summary:

• For simple fractions like halves, thirds, quarters, etc., divide by the denominator.
• For more complex fractions (e.g. two-thirds), divide by the denominator and multiply by the numerator.