Divisibility test are tools to determine if a number can be divided by particular factor. While there are many numbers which are Prime (divisible by the number and 1 only), many more of the numbers we encounter are Composite (divisible by more than 2 numbers). By learning divisibility tests, a person can quickly determine whether (1) a number is composite or prime, (2) the numbers share factors (finding common denominators, LCD), (3) the GCF of a list of numbers, and many other short cuts in arithmetic.

Olsen, Allen. [i]Delving Deeper: Divisibility Tests[/i]. [b]Mathematics Teacher[/b]. pp45-52. Vol. 100, No. 1, Aug. 2006.[br][url=http://www.mathsisfun.com/divisibility-rules.html]MathIsFun[/url] [br][url=http://www.mathgoodies.com/lessons/vol3/divisibility.html]Math Goodies[/url][br][url=http://www.mathplayground.com/howto_divisibility.html]Video Math Playground[/url]