how to find a number is divisible by 5:

 You’ll be happy to know that checking for divisibility by 5 is really easy. The quick and dirty tip is that for a number to be divisible by 5, it must end with either a 0 or a 5. For example, the numbers 5, 10, 15, 20, and so on up to 1,005, 1,010, and on and on forever, are all divisible by 5 since they all end in either a 0 or 5. On the other hand, the numbers 7 and 3,111,428 are not divisible by 5 since they do not end in either a 0 or 5.

Why does this work? Well, the reason is as easy as the tip: It’s simply that no matter what you multiply the number 5 by, the result is always a number that ends in 0 or 5. That’s all there is to it!
 

- See more at: http://www.quickanddirtytips.com/education/math/how-to-tell-if-a-number-is-divisible-by-4-5-or-6#sthash.nhvism2E.