Lesson plan

Fraction Simplest Form by Greatest Common Factor

When fractions have big numerators and denominators, it can be tough to find the simplest form. Fear not! Use this lesson plan to teach your students to find the simplest form using the greatest common factor.
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Students will be able to simplify fractions using the greatest common factor between numerators and denominators.

(5 minutes)
  • Write the following fraction on the board: 2436/3325
  • Ask your students to turn and tell their neighbour a strategy to reduce the fraction to its "simplest form," but don’t clarify the term yet!
  • Allow students to share their ideas with the whole class or with a partner. Note related academic terminology for future reference.
  • Reveal that today’s lesson is about simplifying fractions with larger numerator and denominators by using their greatest common factor. Explain that Simplest formIs when a fraction’s numerator and denominator can no longer be divided evenly by a common factor.
(10 minutes)
  • Hand out and lead your class through the opening model of the Equivalent Fractions and Greatest Common Factor worksheet.
  • Answer any clarifying questions.
(10 minutes)
  • Lead your class through exercise #1.
  • Guide your students through exercise #2, with students reading and offering explanations for as many next steps as possible.
(15 minutes)
  • Release your students to complete the remaining exercises on the worksheet independently.


  • For students needing more practise factoring, have them complete the Greatest Common Factor: Easy worksheet noted in the references section of this lesson plan.


  • Share the strategy for finding if a number is divisible by three. If the sum of the digits are divisible by three, the face value of the number is divisible by three.
    • For example: 363 is divisible by 3, because 3 + 6 + 3 = 12, and 12 is divisible by 3 (12 = 3 x 4).
  • Have students make up fractions with:
    • Numerators and denominators with three to four digits
    • Divisible by three
    • A solution for simplest form
  • Powerpoint and Keynote are great slide show applications for presenting processes one step at a time.
(5 minutes)
  • Show your students a fraction with a single-digit numerator and denominator.
  • Then have them lead you through to an equivalent fraction with a three-digit numerator and denominator.
(10 minutes)
  • Allow your students to share out answers whole class.
  • Discuss: What can simplified fractions tell us about equivalent forms with larger numerators and denominators?

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