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# Using Divisibility Rules

By , About.com GuideJune 24, 2012

A divisibility rule helps you determine if one whole number is divisible by another whole number.  Rules for divisibility are quite helpful as they help you to find factors, help you to reduce fractions and to help you find common denominators.  Although you may not memorize the divisibility rules, you might just want to keep a copy of them handy.

Examples of divisibility rule are:
for a number to be divisible by 2, the number must end in 0. 2, 4, 6 or 8 or
for a number to be divisible by 3, you simply add the sum of the digits and it must be divisible by 3 ( if 21 is the number, the sum of 2 and 1 is 3 which is divisible by 3 or  take 27, 7 + 2 = 9 which is also divisible by 3.

See the full article on Divisibility Rules or watch the video on divisibility math tricks.

July 2, 2012 at 10:20 am
(1) Retired Teacher says:

Deb include what I consider to be a very important disclaimer -”although you may not memorize..”. I always told my students that they should memorize as little as possible, and try to understand as much as possible. I might not remember what the tangent of 30 degrees is, but I can certainly derive it whenever I need it.
Terms like “foil” and “ranbow” really put me on alert. Is the student understanding what is going on, or is the student mastering a “trick”.
Disclaimer -I admit with some shame that I can still find square roots by the old fashioned “pair the digits” method. Certainly some wasted brain cells!

July 5, 2012 at 6:31 pm
(2) Luvisca says:

certainly, some food for thought from a veteran !

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