Divisibility Rules for 6th grade Math

Learn: To use divisibility rules

What’s the point?

These rules let you test if one number can be evenly divided by another, without having to do too much calculation!

Vocabulary

Divisible- Can be divided by a number without leaving a remainder.

Composite Number- Numbers that are divisible by more than two numbers

Prime Numbers- Is a number that is divisible by only numbers 1 and itself.

When will you need to use the rules?

Divisibility rules can be used: to find out if a number is prime

or composite

to help find factors of a number

to find GCF and LCM when dealing with fractions

Divisibility rule for

A number is divisible by 2, if the ones digit is divisible by 2

For example: 746 is divisible by 2… because 6 is divisible by 2

6÷2=3 (hint: any even # is divisible by 2!)

Divisibility rule for

A number is divisible by 3, if the sum of the digits is divisible by 3

For example: 12,321 is divisible by 3 … because 1+2+3+2+1=9 9 is divisible by 3

9÷3=3

Divisibility rule for

A number is divisible by 4, if the number formed by the last two digits is divisible by 4

For example: 824 is divisible by 4… because 24 is divisible by 4 24÷4=6

Divisibility rule for

A number is divisible by 5, if the number ends in a 0 or 5

For example: 120 and 325 are both divisible by 5 120 ends in 0 325 ends in 5

Divisibility rule for

A number is divisible by 6, if the number is divisible by 2 and 3

For example: 36 is divisible by 2 since 6 is even

36 is divisible by 3 since 3+6=9 and 9 is divisible by 3 So, 36 is divisible by 6!

Divisibility rule for

A number is divisible by 7, if you can take the last digit, double it and subtract it from the remaining number and the answer is divisible by 7 For example:203 is divisible by 7… because 3 doubled is 6, and 20-6=14 14 is divisible by 7 14÷7=2

Divisibility rule for

A number is divisible by 8, if the last three digits are divisible by 8

For example:1280 is divisible by 8… because 280 is divisible by 8 280÷8=34 so, 1280÷8=160

Divisibility rule for

A number is divisible by 9, if the sum of the digits is divisible by 9For example:7056 is divisible by 9… because 7+0+5+6=18 and 18 is divisible by 9

18÷9=2

Divisibility rule for

A number is divisible by 10, if the last digit is a zero

For example:100, 240, 3750, 48,720 are all divisible by 10

If you memorize the divisibility

rules, math will become easier!

Let’s review…Write these in your notes! 2 if the ones digit is divisible by 2 3 if the sum of the digits is divisible by 3 4 if the # formed by the last two digits is

divisible by 4 5 if the last digit is a 0 or 5 6 if the # is divisible by 2 and 3

9 if the sum of the digits is divisible by 9 10 if the last digit is a 0