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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.
1,3,5, and 15 are factors of 15 because they can all be divided into 15 without a remainder.
15 has four factors: 1,3,5, and 15.
Problem 1A
Which of the following numbers are factors of 17?
Choose all answers that apply:

All numbers have 1 and themselves as factors.

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 2 factors.
A prime number's only factors are 1 and the number 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.
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.
Problem 2A
Is 13 a prime number?
Choose 1 answer:

Composite numbers

Composite numbers have more than 2 factors.
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.
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.
Problem 3A
Is 15 a composite number?
Choose 1 answer:

The number 1

1 does not fit into either category. It is neither prime nor composite.

Practice with prime and composite numbers

Problem 4A
The numbers 11,17, and 23 are all

Prime number and composite number challenge

Use the clues given to solve the problems below.
Problem 5A
Identify a prime number with 5 in the ones place.
Choose 1 answer:

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