Transcript Identifying Prime & Composite Numbers

Identifying Prime &
Composite Numbers
Coach Lesson 1
Also see textbook pages 14 – 17.
Getting the Idea
The factors of a number are the whole
numbers that divide that number evenly.
For example, to find the factors 8, think about
the whole numbers you can multiply to get a
product of 8.
1 x 8 = 8, so 1 and 8 are factors of 8
2 x 4 = 8, so 2 and 4 are also factors of 8
This means that 8 has four factors: 1, 2, 4, & 8.
A number is a prime number if its only factors
are 1 and itself.
For example, 7 is a prime number because it is
only divisible by 1 and 7.
A number has more than two factors is called a
composite number.
For example, 8 is a composite number since it
has more than two factors.
Note: 2 is the only even prime number. The
number 1 is special. It is neither a prime
number nor a composite number.
Example:
Which of the following is a composite number?
A - 5, B - 11, C - 27, D - 37
Strategy: Test each number.
Step 1: Try Answer Choice A.
The only factors of 5 are 1 and 5. It is a prime number.
Step 2: Try Answer Choice B.
The only factors of 11 are 1 and 11. It is a prime number.
Step 3: Try Answer Choice C.
The factors of 27 are 1, 3, 9, and 27. It has more than two factors. It is a composite
number. Even though C is a composite number, check Choice D just to be sure.
Step 4: Check Answer Choice D.
The only factors of 37 are 1 and 37. It is a prime number.
Coached Example:
Question: Is 33 a prime number or a
composite number?
Thinking It Through:
A prime number has only _______ factors.
The factors of 33 are ______________.
This means that 33 is a _____________
number.