# Activities

• • • ##### Subject Area

• Math: Math General: General

• ##### Author 6-8

60 Minutes

• ##### Device
• TI-73 Explorer™
• ##### Other Materials
This is Activity 5 from the EXPLORATIONS Book:
Discovering Mathematics with the TI-73: Activities for Grades 7 And 8

It's Greek to Me

#### Activity Overview

Students learn Euclid's Method of finding the Greatest Common Factor of large numbers. They also review finding GCF using prime factorization and listing.

#### Before the Activity

• See the attached PDF file for detailed instructions for this activity
• Print pages 39 - 42 from the attached PDF file for your class
• #### During the Activity

Distribute the pages to the class.

Method 1

• Use the Euclid method and the integer divide function on the calculator to find the GCF of the two given numbers
• Divide the larger number by the smaller number
• Successively divide the larger number by the smaller number until the remainder is zero
• GCD is the last divisor

• Method 2
• Write the two numbers as a product of prime factors
• Find the factors common to both and multiply them to get the GCF

• Method 3
• List all the factors for both the numbers
• Find the greatest factor (divisor) common to both, which is the GCF

• Method 4
• Use the GCD function on the calculator find the GCD of the two numbers
• #### After the Activity

Students will complete the Worksheet and analyze the results.

Review student results:

• As a class, discuss questions that appeared to be more challenging
• Re-teach concepts as necessary