Have you ever wondered just how to know when a number can be divided by another? Especially when it's a number that doesn't end in 2, 5 or 0??? Well, there are these great techniques for determining divisibility of a number and I'm going to talk divisibility here, and include some links and videos that can be referenced for further understanding.
First, what is divisibility? Here is the "formal" definition:
For whole numbers a & b, with a not = 0, a divides b if and only if there is a whole number x, so that ax=b. Also, a is a divisor of b or b is divisible by a.
OK, so what does this really mean? In easier terms, think of 20 apples and 10 people - can the apples be divided evenly amongst the people without any being leftover? If so, then 20 is divisible by 10. In this case, if you gave each person one apple, that would use up 10, and there would still be 10. Every person could have another apple, meaning each person gets 2.
20/2=10
Therefore, 20 IS divisible by 10.
That's pretty easy, and if you know your division that one you can do in your head easily. But what about bigger numbers and divisors like 7, 9 or 11? Then things start to get a little more difficult. That's why there are these handy divisibility tests. Here is a link to a list of them:
Math is Fun - List of Divisibility Tests and Examples
Here is a video, too, that shows the divisibility tests in action, if you would rather watch a video or if you're more of a visual learner (like me!):
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