# Divisibility song for 3 and 9 in a relationship

### Divisibility tests for 2, 3, 4, 5, 6, 9, 10 (video) | Khan Academy

9 (nine) is the natural number following 8 and preceding Contents. 1 Mathematics In base 10 a positive number is divisible by 9 if and only if its digital root is 9. The sum of the digits of is 3 + 5 + 9 + 6 + 7 + 9 + 3 + 0 = 42, and . the name derives from "a very curious old semi-pagan, semi- Christian" song. Fun way to learn divisibility rules. Discover ideas about Divisibility Rules . " Engage your students in practicing "long" division with this 9 page project. .. Lesson 3 | Funky Fractions For Fifth Grade Improper Fractions, Teaching Fractions, Teaching Math Paper lip to track where they are in the long division process. Results 1 - 20 of This free product introduces divisibility rules (divisibility tests) with Math Division, Long Division, Math School, 3rd Grade Math, Multiplication songs teaching-classroom-ideas If a student struggles this is a good trick. This file contains a poster to display in your classroom, as well as 9 assignment.

Factors Video transcript What we're going to do in this video are some real quick tests to see if these three random numbers are divisible by any of these numbers here.

### Divisibility Rules for 3 and 9

And I'm not going to focus a lot on the why of why they're divisible-- we'll do that in other videos-- but really just to give you a sense of how do you actually test to see if this is divisible by 2 or 5 or 9 or So let's get started. So to test whether any of these are divisible by 2, you really just have to look at the ones place and see if the ones place is divisible by 2.

And right over here, 8 is divisible by 2, so this thing is going to be divisible by 2. Another way to think about it is if you have an even number over here-- and 0 is considered to be an even number-- then you're going to be divisible by 2.

And over here, you do not have a number that is divisible by 2. This is not an even number, this 5, so this is not divisible by 2. So I won't write any 2 there.

So we've gone through the 2s. Now, let's work through the 3s. So to figure out if you're divisible by 3, you really just have to add up all the digits and figure out if the sum is divisible by 3. So let's do that. So if I do 2 plus 7 plus 9 plus 9 plus 5 plus 8 plus 8, what's this going to be equal to? And 48 is divisible by 3. But in case you're not sure-- so this is equal to in case you're not sure whether it's divisible by 3, you can just add these digits up again.

So 4 plus 8 is equal to 12, and 12 clearly is divisible by 3. And if you're not even sure there, you could add those two digits up. This right over here, let's add up the digits.

And we can do this one in our head pretty easily.

## Divisibility tests for 2, 3, 4, 5, 6, 9, 10

And if you want to add the 1 plus 8 on the 18, you get 9. So the digits add up to 9. So these add up to 9. Well, they add to 18, which is clearly divisible by 3 and by 9, and these two things will add to 9. So the important thing to know is when you add up all the digits, the sum is divisible by 3.

So this is divisible by 3 as well, divisible by 3. And then finally, Let's add up these digits. So we summed up the digits. So this one, we're not going to write a 3 right over there. It's not divisible by 3. And to think about 4, you just have to look at the last two digits and to see-- are the last two digits divisible? Are the last two digits divisible by 4? Immediately, you can look at this one right over here, see it's an odd number.

If it's not going to be divisible by 2, it's definitely not going to be divisible by 4. So this one's not divisible by any of the first few numbers right over here.

## Divisibility Rules for 3 and 9

But let's think about one, Is that divisible by 4? And you can do that in your head. That's 4 times So this is divisible by 4. And then to go from 60 to 70, you have to get another 10, which is not divisible by 4.

So that's not divisible by 4. And you can even try to divide it out yourself. So for a number to be divisible by 6, it must also be divisible by 2 and 3. Therefore, we need to check if a number is even and then check if the sum of the digits is divisible by 3. Determine if the number is even. It ends in 8, so this number is even.

Therefore it is divisible by 2.

Add the digits together. So this number is not divisible by 3. Because this number is only divisible by 2, and not by 3, it is NOT divisible by 6.

This number is even and is therefore divisible by 2. Because the number is divisible by 2 and 3, it is also divisible by 6. The Rule for 9: The prime factors of 9 are 3 and 3. So we can use a very similar rule to determine if a number is divisible by 9. Basically, we will see if the sum of the digits is divisible by 9. If it is, then the actual number is also divisible by 9.

This is done the same way we checked the rule for 3. Determine if 9 goes into 42 evenly. So 9 will not go into 42 evenly. Because 9 goes into 27 evenly, it also goes into 92, evenly. Therefore, 92, is divisible by 9. Using the divisibility tests, we can easily determine if a number is divisible by 3, 6 or 9.