## Tuesday, September 11, 2012

### Speed! - Number Sense - Least Common Denominator

Speed! is a fun game for learning multiplication, but playing Speed! also helps children develop a strong number sense. This is the second post in a new series of posts - Speed! Number Sense - to explore different mathmatical concepts and how playing Speed! can facilitate understanding of these concepts.

The second concept is LEAST COMMON DENOMINATOR. The first step in adding or subtracting fractions is to make sure the denominator of all addends is the same. This is called the least common denominator.

When children play Speed! they begin to notice that some decks have the same numbers as other decks. 12 is a card in Two, Three, Four and Six Speed. That knowledge is an incredible aid in determining the least common denominator.

For example, to add the fractions:

2/9 + 1/4

the first step is to find the least common denominator. Children who have played a lot of Four Speed and Nine Speed should recognize that both decks contain a 36.

It is the fourth card in Nine Speed and the ninth card in Four Speed. It is also the least common denominator.

next
2/9 is multiplied by 1 or (4/4) and 1/4 is multiplied by 1 or (9/9)

2/9(4/4) + 1/4(9/9)

8/36 + 9/36

17/36
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Here is another example:

1/6 + 2/9

the first step is to find the least common denominator. Children who have played a lot of Six Speed and Nine Speed should recognize that both decks contain an 18, 36, and 54.

Since 18 is the lowest number it is the least common denominator. It is the third card in Six Speed and the second card in Nine Speed.

next
1/6 is multiplied by 1 or (3/3) and 2/9 is multiplied by 1 or (2/2)

1/6(3/3) + 2/9(2/2)

3/18 + 4/18

7/18

Playing Speed! doesn't teach adding fractions, it is an activity that helps with multiplication and creates an excellent foundational number sense within children who play. It just makes adding fractions a little bit easier.

#### 1 comment:

1. hi ,,, i just want to share about lowest common denominator

http://www.math-worksheets.co.uk/132-tmd-what-is-the-lowest-common-denominator/