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suggestions on teaching Prime and composite numbers?

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jael1997 jael1997 is offline
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suggestions on teaching Prime and composite numbers?
Old 10-26-2009, 07:26 PM
 
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Hey there! I'm new to fifth grade math. I taught 5th grade LA/SS for two years before being moved to first last year and now am back to 5th grade self contained (all in the same school!) I have to teach math, which I am not the strongest at, and am trying to figure out what to do for Prime and Composite numbers. I know how to DO it, but not how to TEACH it. Any suggestions?


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Manipulatives
Old 10-27-2009, 02:16 AM
 
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I gave out baggies filled with various amounts of cubes. Students would be given one bag and asked to make as many rectangles as possible from the cubes and to record the dimensions.

So, if the bag had 12 cubes they could make 1x12, 2x6, and 3x4, for example. If it had 7, all they could do was 1x7

I put a sheet on the overhead that said "Makes 1 rectangle/Makes 2 or more rectangles," and as they discovered what they could make, they would record their number on the overhead. Again, if the bag had 12 cubes, they would put 12 under "Makes 2 or more."

I led that into a discussion of what a prime number is (2 factors, only one multiplication problem makes it), and a composite (3 or more factors, two or more multiplication problems).

We did the Sieve of Erosthanes as well, and I let them use that as a resource when making factor trees.

A trick the fourth grade teacher taught them was:

prImE has 2 vowels, so it has two factors.

cOmpOsItE has more than 2 vowels, so it has more than two factors.

Have fun!
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Old 10-27-2009, 02:29 PM
 
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There is a good lesson on math live. It also gives practice, my kids really liked it.
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Trick
Old 10-30-2009, 04:18 PM
 
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Can you please explain this trick a little better or provide examples.
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Old 11-01-2009, 07:35 AM
 
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I the same lesson with my 4th graders that twinmom07 explained. The difference is she uses cubes to build arrays and we use grid paper and cut out the arrays. We post the arrays for each number 1-25 on a separate piece of contruction paper and display them. (By the way, each student does NOT do all 25 numbers. Different groups are responsible for cutting out the arrays for certain numbers.) Students label each array with the appropriate expression (or equation if you wish). After all the numbers are displayed around the room -- usually the next day, we go to each number and identify them as prime, composite based on the number of arrays/factors and square based on the shape of the array. Students record all this information on a recording sheet much like twinmom07 uses too.

We leave these displays up all year and refer to them frequently. It's always interesting to hear 4th graders refer to numbers as prime because they only have one rectangle! I have to remind them the rectangle's dimensions are the factors. The brains that grade the BIG STATE test at the end of the year won't necessarily know what they mean by, "A prime number has only has one rectangle."

I also like twinmom07's prImE and cOmpOsItE example. I'm adding it to my lessons from now on. You could probably make up (or have your students make up) a song or a chant to go along with the concept. Right now I'm seeing students squat for the consonants and pop up for the vowels!!!!! A little kinesthetic sometimes works wonders.


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Old 11-04-2009, 07:23 PM
 
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I believe I saw this on proteacher, so I do NOT want to take credit for it.
Prime
Private Party- just one and itself

Composite
Company party-more factors
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Yes and No
Old 11-05-2009, 04:24 AM
 
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I used this lesson just this week with my 4th graders.
Make a T-chart on the board; headings are Yes and No

Under Yes....write a 3
Under No.....write a 4

Ask students what they see about the numbers.
They always say odd/even. I say, okay, let's try it.
Ask them to give you a # and tell you which column to put it in
Record each # in the correct side of the chart I told them the # had to be under 100 because 4th graders love to tell you a million or billion.

Students begin to see patterns...but not prime/composite
Let them work in partners or groups so they can generate more ideas

I did finally give them a clue: hmm, I notice that 9 is the product of 9x1and 3x3 Ask them to work with some of the numbers.

Great discussions...but I did have to explain prime/composite at the end.
It's fun to watch them think!

Last edited by 4strong; 11-05-2009 at 04:26 AM.. Reason: added the limit
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similar trick
Old 11-07-2009, 06:59 PM
 
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This is similar to the PP, but I teach my students that Prime has a Pair of factors and Composite has a Crowd of factors.

I like the idea with the cubes. Gonna steal that one!
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