Prime and Composite Numbers

How can you apply what you know about multiples and factors to determine prime or composite

numbers?

Vocabulary

Prime -

Composite -

Multiple -

Factor - Factor Pair -

any whole number greater than 1 that has two factors. 1 and itself

any whole number greater than 1 that has more than 2 factors

the product of any two whole numbers (can be found by skip counting)the numbers multiplied to find a

product the two factors in a multiplication sentence

How do I find factors?

You could make an array and find the factor pairs!

What about skip counting to find

multiples!

Have you ever heard of a factor

tree?

Do you think you could

show me with 14?

14array

You have 1 group of 14 so the factor

pair would be 1 x 14.

Now let’s see if there

are any equal

groups.

There are two equal groups of 7 so the factor pair is 2 x 7.

factor pairs1 x 142 x 7

factors1, 2, 7, 14

What

abou

t thos

e

fact

or tr

ees?

First let’s recall the factor pairs

for 14.

1 x 14 and 2 x 7

Umm

…m

aybe

we

shou

ld a

sk th

e

class

.Aweso

me! N

ow

what? Now let’s break it

down until we have all primes.

14

>

2 x 7

We used 2 x 7 because the identity

property of multiplication says 1 x 14 and 14 is the

same thing.

We can stop there because 2 and 7 are both prime.

I wonder what a number tree would look like if I had a bigger

number?

481. Count out 48 counters.

2. Break into equal groups.3. Write factor pairs.

4. Try your factor pairs in a factor tree.

>12 x 4

> >

6 x 2

2 x 2

> _ __

3 x 2

2 2 2

5. Multiply your primes to see if you’re correct.

How can we organize this

Make a chart!Number Factor

PairsFactors Prime or Composite

48 • 1 x 48• 2 x 24• 3 x 16• 4 x 12• 6 x 8

1, 2, 3, 4, 6, 8, 12, 16, 24, 48 Composite

I wonder if I used another

factor pair would my

number tree look the same?

48<

6 x 8< <

3 x 2 2 x 4_ _ _ <

3 2 2 2 x 2

No matter the factor

pair you get the same primes.

You give it a try!

Find equal groups. Make

arrays.

Find the factor pairs.

Use the factors in a

number tree.

Number Factor Pairs

Factors Prime or Composite

36

45

24

18

72

Use manipulatives to help you if you

need them.

Go to Stations

Teacher Application Computers Flash Cards

Table 1 Table 2 Table 3 Table 4

Table 2 Table 3 Table 4 Table 1

Table 3 Table 4 Table 1 Table 2

Table 4 Table 1 Table 2 Table 3