Do you remember learning about factors?
Factors are numbers that are multiplied to get a product.
What are the factors of 10?
1 × 10 = 10
2 × 5 = 10
There are no other numbers that we can multiply to make 10.
So the factors of 10 are:
1, 2, 5, and 10
10 has 4 factors. 👏
Prime numbers have only two factors, 1 and themselves. They can't be divided into any smaller parts evenly.
For example, the factors of 7 are just 1 and 7.
1 × 7 = 7
7 × 1 = 7
7 is a prime number. ✅
Another example of a prime number is 11.
The only numbers we can multiply to make 11 is 1 and 11.
1 × 11 = 11
Can you think of more examples of prime numbers? 🤔
There is no easy pattern to find prime numbers. Take a look:
2, 3, 5, 7, 11, 13, 17, 19, 23, 29, 31, 37, 41, 43, 47, 53, 59, 61, 67, 71, 73, 79, 83, 89, 97...
Most numbers have more than two factors.
Numbers with more than two factors are called composite numbers.
The factors of 24 are:
1, 2, 3, 4, 6, 8, 12, and 24.
24 has more than 2 factors.
24 is a composite number. ✅
Is 32 a composite number?
We can easily see that 32 is divisible by 2.
So we know it's a composite number.
Is 13 prime or composite?
We can make 13 by multiplying 1 by 13.
1 × 13 = 13
There are no other numbers that we can multiply to make 13.
13 has only two factors.
So 13 is a prime number. ✅
Let's try one more example.
Is 40 prime or composite?
We can make 40 by multiplying 1 and 40.
That's 2 factors.
We can also multiply:
2 × 20 = 40
4 × 10 = 40
5 × 8 = 40
So 40 has more than 2 factors.
40 is a composite number. ✅
1 has only one factor.
1 is not a prime number, because it has only one factor, while prime numbers must have exactly two factors.
1 is not a composite number because it has only one factor, while composite numbers have more than two!
1 is neither a prime number, nor a composite number.
0 is not a prime number. Only positive numbers, numbers greater than 0, can be prime numbers.
Great job learning about prime and composite numbers.
Now, complete the practice. It'll help you remember what you learned for longer.