Section 4-5 "Greatest Common Factor"

Technology objective: Students will use the TI-34 calculators to find the greatest common factor of a pair of numbers.

Lesson: After a discussion of greatest common factor, ask the students if they can figure out how to use the TI-34 calculator to find the greatest common factor of a set of numbers. Put various suggestions on the board. Next, explain to the students how to use the TI-34 calculator to find the greatest common factor of a pair of numbers. They can do this by entering one number in the place of the numerator and one number in place of the denominator. Have them try to find the greatest common factor of 45 and 60. Have them enter the smaller number in for the numerator, 45, and the bigger number in for the denominator, 60. When the press enter, the calculator will simplify the fraction they entered. Ask the class to figure out what was factored out of the numerator and denominator. (This serves as a great mental exercise.) Once they have figured that number out, they know the greatest common factor. Have them try to find the greatest common factor of any two random numbers. Also discuss what happens when you enter two prime numbers. This can serve as a wonderful introduction to fractions.

Reinforcement:

Game

This game was found in the 1992 Yearbook Calculators in Mathematics Education in the article Statewide In-Service Programs on Calculators in Mathematics Teaching written by Bright, Lamphere, and Usnick. Students should be broken up into pairs. Each pair will be given a 6 x 6 grid with the following numbers inserted in no particular order:

25, 60, 45, 15, 10, 80, 48, 64, 36, 24, 65, 99, 27, 16, 42, 81, 75, 25, 200, 300, 500, 600, 800, 900, 360, 480, 640, 550, 270, 120, 144, 625, 525, 648, 864, and 468.

GCF game

1) Decide who plays first. Play then alternates.

2) On your turn, your opponent chooses an uncovered number on the grid.

3) You then choose a second uncovered number on the grid. Cover both choices.

4) Your score for the round is the GCF of the two numbers.

5) The winner is the player with the greatest cumulative score after five rounds.