Prime Numbers for Kids: Help Kids Learn Prime Numbers

Tips for Teaching Your Child Prime Numbers

Learn About Prime Numbers

In order to explain prime numbers to your child, you must first understand what they are. A prime number is a whole number that can only be divided by 1 and itself. Examples of prime numbers include 2, 3, 5 and 7. Except for 0 and 1, any number that is not a prime number is a composite number. The numbers 0 and 1 are neither prime nor composite because they can only be divided by themselves.

Use a Grid to Find Prime Numbers

This exercise is known as the Sieve of Eratosthenes. Give your child a sheet of paper containing a 10 x 10 grid numbered from 1-100. Black out the square for number 1 because it's neither prime nor composite. Ask if number 2 is composite or prime, and have your child explain why it's prime. Have her circle the 2 square and then write an x over all numbers that can be divided by 2. Point out that this will be every second number, which are even numbers.

Do the same with 3, and show your child that he or she will be crossing out every third number instead of every other number. Continue doing this throughout the chart; some numbers will have already been crossed out. When she has completed the whole chart, 25 prime numbers will be circled, which should include 2, 3, 5, 7, 11, 13, 17, 19, 23, 29, 31, 37, 41, 43, 47, 53, 59, 61, 67, 71, 73, 79, 83, 89 and 97.

Practice

Create flashcards with a series of prime and composite numbers written on them. Quiz your child's knowledge of prime numbers by holding these cards up and asking him or her if these numbers are prime or composite.

You can also reinforce this concept by helping your child create factor trees. Give your child two numbers to work with, such as 31 and 15. Help your child create a factor tree for these numbers. Begin by identifying what two numbers multiplied together to equal 31. The only option is 31 x 1, so draw two lines extending from 31 and write 1 and 31. In this case, the factor tree for 31 will be very skinny because it is a prime number.

Do the same for 15. You can calculate 15 by multiplying 1 x 15 and 5 x 3. As a result, there should be four lines extending from 15, with each of the multiples (1, 15, 5 and 3) written underneath. The tree for 15 will be fatter because it's a composite number.