1. Primes, Factors and Common Factors
Objective: SWBAT find the primes of numbers, the factors of numbers and the common factors from a set of numbers.

2. Vocabulary
Factors numbers you can multiply together to
get another number
Prime
Number a number which only has two factors,
1 and itself
Factors a factor of a number which is also a
prime number
Highest
Common
Factor largest factor between two or more
numbers

3. Rules of Divisibility:
2 – Any number that ends in an even number (0, 2, 4, 6, 8)
in the ones place is divisible by 2.
3 – Add the digits across if you get (3, 6, 9, …) the
number is divisible by 3.
5 – Any number that ends in a 0 or a 5 in the ones place
is divisible by 5.
7 – If the above numbers (2, 3 & 5) don’t work try 7.
If 2, 3, 5 & 7 don’t work the number is probably prime.

4. List all the factors of the following numbers and circle the prime factors.–
1, 2, 3, 6, 11, 22, 33, 66
1, 3, 5, 15, 25, 75
1, 2, 4, 7, 14, 28

5. Find the prime factors of the following numbers
Find the prime factors of the following numbers. Express each number as a product of prime numbers, using indices (exponents) when needed. (Hint: Use a factor tree.)
Answer: 22 ∙ 3
Answer: 26

6. For each of these pairs of numbers: list the factors of each number, write down the common factors and then write down the highest common factor.
6. 14
1, 2, 7, 14 21
1, 3, 7, 21
Common Factors
1, 7
Highest Common Factor 7

7. For each of these pairs of numbers: list the factors of each number, write down the common factors and then write down the highest common factor.
7. 12
1, 2, 3, 4, 6, 12 36
1, 2, 3, 4, 6, 9, 12, 18, 36
Common Factors
Highest Common Factor 12