# Is 21 Divisible By 13?

In this quick and easy guide, we'll work out whether 21 is divisible by 13. There are some simple rules we can follow to decide whether one number is divisible by another without ever needing to even do the division!

First up, let's clarify what we mean by "21 is divisible by 13". What we want to check is whether 21 can be divided by 13 without any remainder (i.e the answer is a whole number).

To check if 21 is divisible by 13, we can remove the last digit from the number, multiply that removed digit by 9 and subtract the answer from the original number. If that resulting number is divisible by 13, then so is 21.

Honestly, it's generally easier to just do the division on a calculator and check if the answer is a whole number but just for fun, let's try and work this out by removing the last digit, 1, multiplying it by 9, and then subtracting the answer from the remaining number:

2

1 x 9 = 9

2 - 9 = -7

In this case, we can see that -7 IS NOT divisible by 13, which means that **21 IS NOT divisible by 13 either.**

Another way you can figure out if 21 is divisible by 13 is by actually doing the calculation and dividing 21 by 13:

As you can see, when we do this division we have a decimal of 0.6154. Since the division does not result in a whole number, this shows us that 21 is not divisible by 13.

Hopefully now you know exactly how to work out whether one number is divisible by another. Could I have just told you to divide 21 by 13 and check if it is a whole number? Yes, but aren't you glad you learned the process?

Give this a go for yourself and try to calculate a couple of these without using our calculator. Grab a pencil and a piece of paper and pick a couple of numbers to try it with.

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