SAT / ACT Prep Online Guides and Tips

Composite Numbers: What Are They? How Can You Spot Them?

Posted by Hayley Milliman | Jan 24, 2019 4:00:00 PM

General Education

 

mika-baumeister-703680-unsplash

Do you know the difference between prime and composite numbers? If not, don’t worry! You’ve come to the right place.

In this post, we’ll talk about what prime and composite numbers are and give you a handy chart you can use to quickly see if something is a composite number.

 

What Is a Composite Number?

Composite numbers are whole numbers that are greater than 1 and divisible by other whole numbers.

Here are the questions to ask yourself to decide if a number is composite:

  • Is the number a whole number?
  • Is the number greater than 1?
  • Is the number divisible by whole numbers other than itself?

Let’s apply those questions to two different numbers to see if they are composite or not.

Take the number “4”.

4 is a whole number. It is greater than 1. You can divide 4 by 4. You can also divide 4 by 2, so it’s divisible by other whole numbers.

That means 4 is a composite number.

Let’s look at the number “3”.

3 is a whole number. It’s greater than 1. You can divide 3 by 3. But, you can’t divide 3 by any other whole numbers.

That means 3 isn’t a composite number.

 

jon-tyson-520850-unsplash

 

How to Tell the Difference Between Prime and Composite Numbers

If a number isn’t composite, then it’s prime. Prime numbers are numbers that are greater than 1 that are only divisible by themselves and the number 1.

The best way to tell if a number is prime or composite is to perform the divisibility test.

When you use the divisibility test, you check to see if a number is divisible by common prime factors, like 2, 3, 5, 7, 11, and 13.

If you’re testing an even number, start by trying to divide it by 2 to see if it’s composite.

If you’re testing a number that ends with 0 or 5, try to divide it by 5.

If you get a whole number when dividing by any of these common factors, then your number is composite.

If you get a fraction or decimal when dividing by these common factors, then your number is likely prime.

 

Composite Number Chart (1-100)

Here is a handy composite number list to reference. All of the numbers in blue are composite numbers.

compositenumberchart 

 

Prime Number Chart (1-100)

Here’s an easy-to-reference prime number list. All of the numbers in red are prime numbers.

primenumbers 

 

Final Thoughts

It’s important to know whether a number is prime or composite so you can understand whether or not the number is divisible.

Remember, ask yourself these questions to tell if a number is a composite number or not:

  • Is the number a whole number?
  • Is the number greater than 1?
  • Is the number divisible by whole numbers other than itself?

 

What’s Next?

Writing a research paper for school but not sure what to write about? Our guide to research paper topics has over 100 topics in ten categories so you can be sure to find the perfect topic for you. 

Learning about natural logs? Check out our guide on the 11 natural log rules you must know to ace this subject.

What is dynamic equilibrium and what does it have to do with rusty cars? Find out by reading our complete guide to dynamic equilibrium. 

 

Have friends who also need help with test prep? Share this article!
Hayley Milliman
About the Author

Hayley Milliman is a former teacher turned writer who blogs about education, history, and technology. When she was a teacher, Hayley's students regularly scored in the 99th percentile thanks to her passion for making topics digestible and accessible. In addition to her work for PrepScholar, Hayley is the author of Museum Hack's Guide to History's Fiercest Females.



Get Free Guides to Boost Your SAT/ACT
100% Privacy. No spam ever.

Ask a Question Below

Have any questions about this article or other topics? Ask below and we'll reply!