Main content

### Course: 4th grade > Unit 6

Lesson 2: Prime and composite numbers# Prime and composite numbers intro

Learn about prime and composite numbers and practice identifying them.

## Let's review factors

Factors are whole numbers that can be divided evenly into another number.

**All numbers**have

## Categories of numbers

We can divide almost all numbers into two categories: prime numbers and composite numbers.

### Prime numbers

Prime numbers are numbers with exactly

**factors.**$2$ A prime number's only factors are ${1}$ and the number ${\text{itself}}$ .

**prime**number. Its only factors are

Let's use pictures to visualize prime numbers.

Farmer Maxwell is making a chicken coop for his best egg laying hens. He has $7$ hens and is thinking about how he can arrange them. He wants to arrange the hens in equal sized groups.

The only possibility is to make $1$ row of $7$ hens.

Any other arrangements would not have the same number of hens in each row.

When there is only one possible way to divide a number into equal sized groups, that number is prime.

## Composite numbers

Composite numbers have more than $2$ factors.

**composite**number. The factors of

Let's use pictures to visualize composite numbers.

Farmer Maxwell is also inventing a new egg carton where he will store the eggs his hens lay. He wants each carton to hold $16$ eggs.

He could have $1$ row of $16$ eggs.

He could also have $2$ rows with $8$ eggs in each row.

Or he could have $4$ rows with $4$ eggs in each row.

Composite numbers have more than one way that they can be divided into equal groups.

### The number $1$

## Practice with prime and composite numbers

## Prime number and composite number challenge

Use the clues given to solve the problems below.

## Want to join the conversation?

- Is 0 an even number or an odd(46 votes)
- Zero is an even number. In other words, its parity—the quality of an integer being even or odd—is even. ... Not only is 0 divisible by 2, it is divisible by every power of 2, which is relevant to the binary numeral system used by computers. In this sense, 0 is the "most even" number of all.(26 votes)

- Why is one not prime nor composite? What is it called?(16 votes)
- 1 is not composite because 1 does not have more than 2 factors, and all composite numbers have more than 2 factors.

1 is not prime because prime numbers are divisible by 1 and the number itself. 1 only contains itself and no other number. 1 belongs to its own unique category named "units."(27 votes)

- Is every even number a composite number because every even number has a factor of 2 except for 0 and 2.(11 votes)
- Yes, all even numbers except 2 and zero are composite numbers.

Zero is neither prime nor composite.(23 votes)

- is 0 prime or composite? because it said nothing about 0.(11 votes)
- it is neither because.., 0 isn't a natural number(16 votes)

- Can all prime numbers be odd?(7 votes)
- 2 is the only even prime number because every other even number is divisible by 2. All other prime numbers are odd.(12 votes)

- i dont understand the last one(9 votes)
- Well, five itself is a prime number, but anything else with 5 in ones place is a composite number.(6 votes)

- But isn't 1 kind of like prime?(6 votes)
- A prime number has exactly 2 factors: itself and 1.

The number 1 has only one factor, itself. So it doesn't satisfy the definition of being a prime number.

Hope this helps.(12 votes)

- This might sound weird. I get the topic but i don't fully understand it. Can someone explain the topic a but more simple?(1 vote)
- A Prime number is a whole number greater than 1 with only two factors – itself and 1, like
**2 x 1 = 2**that means 2 is a prime number, because 2 and 1 are the only factors that can make 2. But a Composite number is different, because the number has more factors than only 1 and itself. So when a number like 4 comes along, and the factors are 1, 2, and 4, which means it's a Composite number. Does that help or do I need to explain it a little more?(22 votes)

- After every question I got right I barked, "WHOOP WHOOP".

Even my mom could here me from downstairs. 😂(11 votes)