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Course: 4th grade (2018 edition)>Unit 7

Lesson 2: Prime and composite numbers

Prime and composite numbers review

Review prime and composite numbers, and try some practice problems.

What are prime numbers?

Prime numbers are numbers with exactly $2$ factors.
A prime number's only factors are $1$ and the number $\text{itself}$.
$7$ is an example of a prime number. Its only factors are $1$ and $7$. It is not evenly divisible by any other whole numbers.

Practice set 1: Identifying prime numbers

Problem 1A
Which of these numbers is prime?

Want to try more problems like this? Check out this exercise.

What are composite numbers?

Composite numbers have more than $2$ factors. A composite number has factors in addition to $1$ and the number $\text{itself}$.
$16$ is an example of a composite number. The factors of $16$ are $1,2,4,8$ and $16.$ All of these numbers divide into $16$ evenly.

Practice set 2: Identifying composite numbers

Problem 2A
Which of these numbers is composite?

Want to try more problems like this? Check out this exercise.

Want to join the conversation?

• How did scientists discover about prime numbers
Edit: that was a weird question….
• I actually have no idea. But I imagine that a mathematician found out that some numbers can only be divided by one and itself. But I am not sure.
• is 2 the only even prime number
• Yes because all other even numbers are divisible by 2
• One question about this: is 1 a prime or a composite number? Neither of those numbers.
• Its a neither because it is cannot be divisible by 2 natural number or it has only on factor
• Is 1 a prime number or a compsite number?
• It is neither prime nor composite because it's only factor is 1.
• is 349,860,748,398 a composite or prime?
• Composite. It is divisible by other numbers than 2, such as 3.
• Why is 2 the lone even prime number?
• A number is prime only if it can be divided by 1 and itself. Because the only factors of 2 are 1 and 2, 2 matches the definition of a prime number and is, therefore, prime.
• whats the point of learning about prime and composites if no one really uses them outside of school?