Finding the Greatest Common Factor for a Set of Numbers

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Author: Cynthia Niles
School District: Diocese of Ogdensburg
Subject: Mathematics
Grade Range: 5
Duration/Time Required:

  • Number of days: 1
  • Length of period: 30 - 45 minutes

Standard: 3 Mathematics

  • Content - Number Sense & Operations: N.14 and N.15
  • Process - Communication: CM 4 and CM 6

Objective:
Students will:

  • Find the common factors and the GCF for a set of numbers.
  • Work cooperatively in groups.
  • Write their own GCF problems.

Instructional Plan:

  • Review previous material by using a math problem of the day (bell ringer). Give students five minutes to answer the math problem. Collect students’ papers and choose a set of partners to come to the board to solve the problem. They must also explain how they got their answer. Review the concept of common factors for a set of numbers. Introduce the definition of greatest common factor (GCF) on the board. Use the numbers 6 and 8 to demonstrate the concept. Divide the class into two groups. Distribute the index cards with the numbers and factors to each group. (Group 1: 9 and 24). (Group 2: 12 and 18). Students will work cooperatively in their group, matching the factors to each number and determine the greatest common factor for both numbers. Groups will need to record their answers for each set of cards. After students have completed this task, switch cards so that each group has the other group’s numbers. Once each group has completed the task of finding the greatest common factor for each set of numbers, add another number to the set of cards. Each group will have to find the factors for the new number before they can find the GCF of the three numbers. Once each group has completed this task have students work individually and create their own set of numbers, using three numbers. Students must find the factors and GCF of each set. If time allows have students switch their GCF problem with their partners. Partners will then solve the problem by finding the factors and GCF for the set of numbers.

Homework: Create a GCF problem using a set of four numbers.

Assessment:

  • Students understanding of common factors and GCF.
  • Group cooperation.
  • The ability to create their own GCF problem.
  • Completion of the homework assignment.

Resources:

  • Student resources: math notebook
  • Materials: pencils, paper, the numbers 9, 12, 18, 24 written individually on index cards, and the factors for each number written on separate index cards.