# Divisibility rules

Is the number prime or composite? 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.

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. 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?Divisibility rules are efficient shortcut methods to check whether a given number is completely divisible by another number or not.

These divisibility tests, though initially made only for the set of natural numbers. Buy Divisibility Rules of Whole Numbers Made Simple on metin2sell.com FREE SHIPPING on qualified orders. A divisibility rule is a shorthand way of determining whether a given integer is divisible by a fixed divisor without performing the division, usually by examining its digits.

Although there are divisibility tests for numbers in any radix, or base, and they are all different, this article presents rules and examples only for decimal, or base 10, numbers. Divisibility rules help us work out whether a number is exactly divisible by other numbers (i.e.

there is no remainder). The rules are shortcuts for finding out whether numbers are exactly divisible without doing division calculations. Jul 03,  · Worked example of basic divisibility tests Practice this lesson yourself on metin2sell.com right now: metin2sell.com A divisibility rule is a shorthand way of determining whether a given integer is divisible by a fixed divisor without performing the division, usually by examining its digits.

Although there are divisibility tests for numbers in any radix, or base, and they are all different, this article presents rules and examples only for decimal, or base.

Divisibility rule - Wikipedia