[catapult]

any ideas for how to teach GCF... I have never taught it yet- and I want my kids to understand it well... (also how do I explain to my students what factors are- in a clear way?)

[Phyllis]

Just like addends are the numbers you add together to get a sum, factors are the numbers you can multiply together to get a product. Every number has at least two factors: the number itself and one:

7: 1, 7 Numbers with only those two factors are called prime numbers. 3, 5, 7, 11, 13, 17, 19 are some prime numbers.

Some examples of numbers with more factors:
12: 1, 2, 3,4,6, 12
20: 1, 2, 4, 5, 10, 20
15: 1, 3, 5, 15

I would do many examples like these on the board and then give them some examples to do on their own:

8: __ __ __ __
36: __ __ __ __ __ __ __ __ __

After they have shown that they can do this, it's time to give them some numbers to find the largest common multiple for.

9: 1, 3, 9
15: 1, 3, 5, 15 3 is the largest common multiple

28: __ __ __ __ __ __
42: __ __ __ __ __ __ __ __ This is a good example of another
they could be given.

[DaisyLilli]

We used factor rainbows...hard to explain, but google and it will give you pictures and explainations. We would make a rainbow for each number (like 12 and 32) and then circle all the numbers that were the same (factors) and then put a star on the gcf.

It was great for different types of learners since it could be easily color-coded if needed.

[Linda/OH]

I just googled it and find it very cool! I tried out a few to see how to make them and what they'll look like.

Question: what happens to single numbers that don't connect to another number as in the case of 10 as a factor of 100? or 3 as a factor of 9?

[Linda/OH]

I found my own answer:
http://edtech2.boisestate.edu/brianr...torrainbow.jpg