How to Teach Elementary Divisibility Rules in Math

As students are learning about division, they learn that some numbers are divisible by other numbers, while others have a remainder. There are divisibility rules that can help students figure out whether a number is divisible by another number easily, without going through all of the steps of long division.

Things You'll Need

• Chalk
• Blackboard

Instructions

1. Explain to students that a number is only divisible by 10 if it ends in a "0." Explain that a number is only divisible by 5 if it ends in a "5" or a "0."

2. Write a list of numbers on the board--some ending in 5, some ending in 0, and some ending in a different number. Challenge students to come to the board and circle the numbers divisible by 10. Then have them put a check next to the numbers divisible by 5.

3. Explain to students that a number is only divisible by 2 if it ends in an even number: 2, 4, 6, 8 or 0. Then challenge students to come up with a number that is divisible by 5, 10 and 2.

4. Tell a child that you can tell if a number is divisible by 3 by adding up the digits and seeing if the sum can be divided evenly by 3. Give the students sample numbers with several digits and ask them to identify the ones that are divisible by 3.

5. Tell a child that you can tell if a number is divisible by 9 by adding up the digits and seeing if the sum can be divided evenly by 9. Ask students which other number has similar divisibility rules to 9. Give students sample numbers with several digits and ask them to identify the ones that are divisible by 9.

6. Explain to students that you can tell if a number is divisible by 4 by seeing whether the last two digits of the number are divisible by 4. Give students sample numbers with several digits and ask them to identify the ones that are divisible by 4.

7. Explain to students that you can tell if a number is divisible by 8 by seeing whether the last three digits of the number are divisible by 8. Ask students which other number has similar divisibility rules to 8. Give students sample numbers with several digits and ask them to identify the ones that are divisible by 8.

8. Explain to students that you can tell if a number is divisible by 6 by figuring out if it is divisible by both 2 and 3. Any number that is divisible by both is also divisible by 6. Have students explain the steps they would take to find out if a number is divisible by 6.

9. Tell students that there is no divisibility rule for 7. To figure out if a number is divisible by 7, you have to divide the entire number by 7 and see if it divides evenly.

10. Review the divisibility rules with students by giving them several very long numbers and figuring out which numbers it is divisible by.

Tips & Warnings

• You may want to review the divisibility rules with students more frequently if they are having difficulty remembering them. You can make a chart with each of the nine numbers in one column and the divisibility rule for that number in the second column.