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Background For Teachers:
In the case of adding or subtracting, unlike fractions, the Least Common Multiple (LCM) needs to be found. The dominos in this activity illustrate the need for a common or matching set of dominos in order to add. That is where we need the common denominator.
As a teacher, you can even explain the use of the term common
denominator in everyday speech. For example, the common denominator
in the Civil War was hatred of each side for the other. That is what was
shared in common—the common cause of the war.
Intended Learning Outcomes:
Have pairs or small groups of students set up two unequal lines of dominos standing on their short end. They can use straight lines or curves—as long as the lines have an unequal amount with a difference of at least three.
When the lines are set up, have students tip them at the same time. What do they notice? Did the shorter line finish first? Of course. They are not even. One line has more than another. Explain that you will use the dominos to add unlike amounts of fractions together.
Tankersley, K. (1993). Teaching Math Their Way. Educational Leadership, 50, 12-13.
This article follows the development of a methodology of using manipulatives for elementary math that fosters discovery and positive attitudes toward math. It also reflects an increase in testing results in math.
Rust, A. L. (1999). A study of the benefits of math manipulatives versus standard curriculum in the comprehension of mathematical concepts. Knoxville, TN, ERIC 436395.
This dissertation attempted to test first graders using both standard text-book based instruction and the use of manipulatives in math. Conclusions indicated little difference in tested results, though standard curriculum methods did show slightly higher results. However, the article points out that students’ enjoyment of the different methods wasn’t studied.
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