1. Bell Ringer What is a prime number? What is a composite number?
Give an example of each.

3. Greatest Common Factor
Mr. Haupt
CC E.1

4. Greatest Common Factor
The Greatest Common Factor, or GCF, is the largest number that goes in to every number given.
For example, the GCF of 12 and 16 is 4.
To find the GCF, you need to know the difference between prime and composite numbers.

5. Prime Numbers
Prime numbers are numbers where the only factors, or ways to multiply, are one and the given number.
For example, the number 17 can only be broken down into one times 17.
Other examples: 1, 2, 3, 5, 7, 11, 13, 19, 23, 31, etc…

6. Composite Numbers
Composite numbers are basically numbers that are not prime.
So, they are numbers that have more multiples than just one and itself.
For example, the factors of 28 are:
1 x 28
2 x 14
4 x 7

7. Prime or Composite? 89 21 33 97

8. Prime Factorization
Prime Factorization is breaking a number down into its smallest (prime number) factors.
I find it easiest to use a factor tree.

9. What if we add letters?
Nothing changes, except now we have to write out the letters.
45a2b c3d

10. GCF, finally! So finally, we can get to the actual GCF.
To find the GCF, we have to do the prime factorization of each number given.
Then we take all the prime numbers they have in common, and multiply them.
Our answer is the GCF.

11. For example…
Find the GCF:
36 and 45
28a2b and 35ab2

12. A few more…
88 and 44
64a2b2 and 96a2b