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Math Help - Tricks with division

  1. #1
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    Sep 2005
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    Tricks with division

    Sup everyone, this is my first post... this seems to be a cool forum so I'm glad to have found it.

    Well, anyways the point of this post was because i was helping my little brother with his math homework (I'm 19) and i think i found a very very easy way to know if a number is divisible by 4. I looked at many places with division tricks and i never saw this one so here it goes:

    The first thing you have to keep in mind is that the Prime Origin of 4 is 2 * 2 which means that only even numbers can be divided by 4.

    Now,

    Lets take for example the number 41434098709812738

    Look at the last digit of number you got. In this case the last digit is 8, which is even, so you may wanna check if its divisible by 4.

    Here is the trick: if the last digit is 2 or 6, then it will be divisible by 4 if the second to last digit is odd; and if the last digit is 0, 4 or 8, then it will be divisible by 4 if the second to last digit is even. Therefore our number 41434098709812738 is not divisible by 4 because it ends in 8 and the second to last digit is odd and not even.

    Cool huh, now you dont need to check if the last 2 digits are divisible by 4 like the common rule.

    I like looking for tricks and patters in math so i hope to be posting more soon... In case the Admins want to make a new section for tricks please move this post to that section.

    Take care everyone and hope to be around again soon

    - Luke
    Last edited by Luke; September 15th 2005 at 10:06 PM. Reason: changing title to be more accurate to post
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  2. #2
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    Joined
    Sep 2005
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    6

    Here's an easy way to know if the number is divisible by 8

    not that in order for a number to be divisible by 8 it must first of all be divisible by 2, that is it has to be even.

    take a number lets say 1456896

    separate the last 3 digits of the number and forget about the rest

    now you have 896

    divide the last digit by 2 and add it to the new number

    896 + (6/2) = 892

    now check if this last number (892) is divisible by 4 using the rule i gave on the previous post. look at the last digit, if its 2 or 6 the number will be divisible by 4 if the second to last digit is odd, the last digit is 2 and the second to last is odd and thus 1456896 is divisible by 8.
    Last edited by Luke; September 15th 2005 at 10:12 PM. Reason: making it even simpler
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