How to identify whole numbers that are prime or composite

What is the smallest positive number?

The smallest positive number is 2.

So, the fist step of how to identify whole numbers that are prime or composite is to divide that number by 2. What do you get?

In this example, we divide 10 by 2. The answer is 5. What does this mean? It means 10 has more than 2 factors: 1, 2, 5, and itself. Therefore, 10 is a composite number and not a prime number. For whole numbers such as 10, all you need to know to identify prime numbers and composite numbers is the first step of how to identify whole numbers that are prime or composite.

However, if you are faced with a whole number that the smallest whole number (2) cannot divide into, then you should move onto the second step of how to identify whole numbers that are prime or composite. For example, let's consider 21.

How to identify whole numbers that are prime or composite Step 2

21 is clearly not divisible by 2 since dividing 21 by 2 gives 10.5 which is not a whole number.

The second step of how to identify whole numbers that are prime or composite is to divide the number (in this case 21) by the next smallest prime number. The next smallest prime number is 3, therefore, divide 21 by 3. What do you get?

Dividing 21 by 3 gives 7. That means, 21 has more than 2 factors: 1, 3, 7, and 21. That means 21 is a composite number and not a prime number.

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