Welcome to another important pre-algebra lesson. In this video, we will be looking at the rules for divisibility of numbers.

A Number is said to be divisible by another number, if it can divide the number without a remainder.

Example

4 is divisible by 2. Because when we divide 4 by 2 we will get exactly 2. With no remainder.

For most small numbers it is easy to know the divisibility by just knowing your multiplication table. The problem is when the number gets larger.

The following rules will help you know the divisibility of some numbers.

It will be good to copy it down because we will be using it again in this lesson.

 

Divisible by 2

A number is divisible by two if the number is even.  Even numbers are 2, 4, 6, 8, 10, 12 and so on.

Another way I look at this is:  if the unit digit is 0, 2, 4, 6 or 8, then it is divisible by 2

Example

456 is divisible by 2 because the unit digit is 6

60 is divisible by 2 because the unit digit is 0.

Hope you get the picture.

 

Divisible by 3

A number is divisible by three if the sum of the digits is divisible by 3.

Example

27 is divisible by three because when you add the digits, 2 and 7, you will get 9.

And we know that 9 is divisible by 3.

Example 2

156 is divisible by 3, because when you add 1 + 5 + 6, you will get 12.

12 can be divided by 3 with no remainder.

Please note that this is not the answer. It only shows it is divisible. If you do the actual division your answer will be 52

 

Divisible by 5

A number is divisible by 5 if the unit digit is 5 or 0.

Example

95 is divisible by 5 because the unit value is 5.

Again 230 is divisible by 5 because the unit digit is zero.

 

Divisible by 6

A number is divisible by 6, if it is divisible by both 2 and 3.

Example

Let’s check if 234 is divisible by 6.

For this to be true, we first check if it divisible by 2.

We know it is divisible by 2 because it is an even number or because the unit value is 4.

Now let’s check if it is divisible by 3

We know it is divisible by 3 if the sum of its digits is divisible by 3. When we add 2 + 3 + 4, we get 9. Which is divisible by 3.

Now since it is divisible by both 2 and 3, we can say it is divisible by 6.

 

Divisible by 9

A number is divisible by 9 if the sum of the digits is divisible by 9.

Example

567 is divisible by 9 because when we add 5 + 6 + 7, we get 18, which is divisible by 9.

 

Divisible by 10

A number is divisible by 10 if the unit digit is zero.

This is pretty straight forward.

So 130 is divisible by 10 because it has zero as its unit value.

This brings us to the end of this video. It’s ok to memorize this because it’s actually easy to remember.

Have a great day. Good bye.