# Prime and Composite Numbers — Let's Practise!

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## Basics on the topicPrime and Composite Numbers — Let's Practise!

Join Razzi to practise finding prime and composite numbers.

### TranscriptPrime and Composite Numbers — Let's Practise!

Razzi says get these items ready because today we're going to practise Prime and Composite Numbers It's time to begin! List all of the factor pairs of the following numbers to determine if the number is prime or composite. Is twenty-six, PRIME or COMPOSITE? Pause the video to work on the problem and press play when you are ready to see the solution! The factor pairs of twenty-six are one and twenty-six and two and thirteen. Did you also get that twenty-six is COMPOSITE? Let's tackle the next problem! Is thirty-one, PRIME or COMPOSITE? Pause the video to work on the problem and press play when you are ready to see the solution! The factor pairs of thirty-one are one and thirty-one. There are no more factor pairs. Did you also get that thirty-one is a PRIME number ? Let's tackle the next problem! Is the number seventy-seven, PRIME or COMPOSITE? Pause the video to work on the problem and press play when you are ready to see the solution! The factor pairs of seventy-seven are one and seventy-seven and seven and eleven. Did you also get that seventy-seven is a COMPOSITE number? Let's tackle the final problem! Is ninety-seven, PRIME or COMPOSITE? Pause the video to work on the problem and press play when you are ready to see the solution! The factors of ninety-seven are one and ninety-seven. There are no more factor pairs. Did you also get that ninety-seven is PRIME ? Razzi had so much fun practising with you today! See you next time!

## Prime and Composite Numbers — Let's Practise! exercise

Would you like to apply the knowledge you’ve learnt? You can review and practice it with the tasks for the video Prime and Composite Numbers — Let's Practise!.
• ### What are prime and composite numbers?

Hints

9 is a composite number. Its factors are 1, 3, and 9:

• 1 x 9
• 3 x 3
3 is a prime number. Its factors are 1 and 3:

• 1 x 3

Make a list with all the factors of 12 and 7.

The prime number will have fewer factors than the composite number.

Solution

1. A prime number has only two factors - 1 and itself.
2. A composite number has more than two factors.
3. 12 is a composite number.
• 12 is composite because it has more than 2 factors: 1, 2, 3, 4, 6 and 12.
4. 7 is a prime number.
• 7 is prime because it has only 2 factors: 1 and 7 (itself).

• ### Say whether 45 is prime or composite by listing all factors.

Hints

Let's do one together.

3 is a factor of 45. How many times does 3 go into 45?

3 goes into 45 15 times. So, 15 is a factor of 45.

Remember, a number is prime when it has only 2 factors: 1 and itself.

How many factors did you find for 45?

Solution

The factor pairs of 45 are:

• 1 x 45
• 3 x 15
• 5 x 9
45 is composite.

• ### Answer the questions and fill in the missing factors.

Hints

Let's complete the factor pair 3 x ? = 99.

First, find out how many times 3 goes into 99.

3 goes into 99 33 times. So, 33 is the missing factor in the pair.

Can you find the other factors?

A prime number has only two factors: 1 and itself.

A composite number has more than two factors.

Apply these rules to the factors you found for 83, 99 and 63.

Solution

83: There are 2 factors, 1 and 83.

99: The factor pairs of 99 are:

• 1 x 99
• 3 x 33
• 9 x 11.
63: The factor pairs of 63 are:
• 1 x 63
• 3 x 21
• 7 x 9.
The prime number in the image is: 83.

The composite numbers in the image are: 99 and 63.

• ### Help Razzi find all the factors for the numbers below.

Hints

Start by finding all the factor pairs of 65. Can you fill in the missing factors?

1 x ?

5 x ?

Let's list the factor pairs of 52. Can you find the missing factors?

1 x 52

? x 26

4 x ?

For the last three gaps, use the numbers 65, 67 and 52.

Solution

65

• The factors of 65 are: 1, 5, 13, 65
67
• The factors are: 1 and 67
52
• The factors are: 1, 2, 4, 13, 26, 52

The prime number is 67.

The composite numbers are 52 and 65.

Hints

Let's find the missing factor in the pair ? x 8 = 16.

Here, 16 has been split up into groups of 8, how many groups are there?

There are 2 groups of 8 in the image so 2 x 8 is a factor pair of 16.

Remember:

You can check if a number is prime or composite by how many factors it has.

If it has more factors than 1 and itself, it's composite.

Solution

The factor pairs of 17 are: 1 x 17.

17 is prime.

The factor pairs of 16 are:

1 x 16

2 x 8

4 x 4

16 is composite.

• ### What are the prime numbers between 30 and 40?

Hints

Remember, a prime number only has two factors: 1 and itself.

Let's find the factors of 32 together.

The factor pairs of 32 are: 1 x 32, 2 x 16, 4 x 8. There are six factors.

So, 32 cannot be prime because it has more factors than just 1 and itself.

Remember, if a number has more than 2 factors it must be composite.

The even numbers between 30 and 40 cannot be prime because they have 2 as a factor!

Solution

The prime numbers between 30 and 40 are: 31 and 37.