Is It A Prime Number, Yes or No?

Jonathan Brinkerhoff

There are different kinds of numbers.

You know about whole numbers, like 5, and fractions like ⅓.

You know about odd and even numbers.

Today, we’ll learn about another kind of number – prime numbers.

I’m going to show you some numbers.

Some are prime and some are not.

When you think you know what makes a number prime or not, raise your hand.

3 is a prime number

3 = 1 X 3

4 is not a prime number

4 = 1 X 4

4 = 2 X 2

5 is a prime number

5 = 1 X 5

6 is not a prime number

6 = 1 X 6

6 = 2 X 3

7 is a prime number

7 = 1 X 7

12 is not a prime number

12 = 1 X 12

12 = 2 X 6

12 = 3 X 4

13 is a prime number

13 = 1 X 13

15 is not a prime number

15 = 1 X 15

15 = 3 X 5

What do you think a prime number is?

You figured out that a prime number has only two factors, itself and 1.

Let’s Practice!

If it’s a prime number

If it’s not a prime number

8

9

14

17

21

10

19

You can correctly identify prime numbers.

2 is a prime number

2 = 1 X 2

9 is not a prime number

9 = 1 X 9

9 = 3 X 3

11 is a prime number

11 = 1 X 11

14 is not a prime number

14 = 1 X 14

14 = 2 X 7

What do you think a prime number is?