Primes and Divisability Rules

Hi Ellie,

That was great news! I'm glad to hear this blog is helping you in your math class. You asked for some stuff about prime numbers and I've got it for you. Before we get to that could you let me know how you're doing with the things I've already posted here for you. In particular I'd like to know how many of the addition and subtraction and multiplication practice you're getting right in one minute. If you don't want to post it here that's OK, you can email me. It will be really helpful to me to know this so I can give you exactly the kind of help you need. ;-) Here is another multiplication game. If you get 20 right in 60 seconds or less you get a prize!

The last link I left you in the first post below had this link which is a really good lesson on prime numbers. If you haven't worked through it yet now would be a good time to do so. ;-)

One of the reasons we need to know about primes is to find the prime factors of a number. Over there --> in the links list on the sidebar you'll find a couple of links to math dictionaries. Look for the definition of:

• factor


• prime number


• composite number


• prime factor

Copy them and email them to me. It might be a good idea to get a notebook to use for our work together. Let's keep track of all the definitions we learn (like the four above) in that notebook OK? We'll call it "Ellie's Math Dictionary."

Your teacher has also probably talked to you about Divisability Rules. These are little "tricks" we can use to test which numbers divide another number evenly. Read this list of divisability rules and copy them into your math dictionary. The ones for 2, 3, 4, 5, 6, 8, 9 and 10 are really important to memorize. We'll put the others (7, 11, 12 and 13) in our dictionary too just in case you ever need to look them up. ;-)

If you come across any words you don't understand, look them up in the dictionary links and copy the new words into "Ellie's Math Dictionary" -- please let me know about any new words you add to your dictionary.

When you're done with your dictionary (keep it open next to you) go here and scroll down the page to the examples. Read through them all carefully and then you'll find a five question quiz to see how well you understand what you've learned -- let me know how you did.

If you haven't already you're probably getting ready to learn about the G.C.F. (Greatest Common Factor) and the L.C.M. (Least Common Multiple). Don't worry if you don't know what those things are just yet -- we'll get there. ;-) Play with a factor tree game at this site. Scroll down the page until you see the Factor Tree link and click it.

Again, please email me and let me know how you're doing with the stuff I talked about way back in that first paragraph up there ^.