In this lesson, students used Cuisenaire rods to explore the idea of common multiples and least common multiples. Each Cuisenaire rod corresponds to a different number based on how many centimeters long it is. Brown corresponds to 8, purple is 4 and dark green is 6. Students lay the Cuisenaire rods down on centimeter grid paper to see where the rods meet. They use skip counting to label the numbers (the brown count by 8, the purple count by 4, the dark green by 6). The students glued the die-cuts on the graph paper, alternating between the rod color and a neutral color to make the activity more visual. Students start to understand the concept that common multiples are where the numbers meet. For instance, when you count by 4 and count by 8, the first time the patterns meet is at 8. When you count by 4 and by 6, the first time the patterns meet is at 12. When you count by 4, 6 and 8, the first time all three patterns meet is at 24. Where the patterns meet for the first time is the Least Common Multiple.
In Ms. Flory's class, students used an alternate method for understanding least common multiples. This student used two number lines, one to show the multiples of 6 and one to show the multiples of 9. On the top number line, the student skip counts by 6. On the bottom number line, the student skip counts by 9. The student then circles the multiples they share, or the common multiples. The concept of the least common multiple is understandable because, in this case, 18 is the first multiple that 6 and 9 share.
This example shows the least common multiple of 4 and 6.
Indicator: 6.5.3.3 find the greatest common factor and the least common multiple
of numbers.
