Download Primes, Factors and Common Factors

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.
Vocabulary
Factors
Prime
Number
Prime
Factors
numbers you can multiply together to
get another number
a number which only has two factors,
1 and itself
a factor of a number which is also a
prime number
Highest
Common
Factor
largest factor between two or more
numbers
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.
List all the factors of the following numbers and
circle the prime factors.
1. 66 –
1, 2, 3, 6, 11, 22, 33, 66
2. 75 1, 3, 5, 15, 25, 75
3. 28 1, 2, 4, 7, 14, 28
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.)
4. 12
3
5.
4
2
64
8
2
Answer: 22 ∙3
2
8
4
2
2
2
4
2
Answer: 26
2
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
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
1, 2, 3, 4, 6, 12
Highest Common Factor
12