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    #7321 - 01/15/08 05:35 PM Multiplication and Other Math Tricks
    questions Offline

    Registered: 11/24/07
    Posts: 864
    Someone here referenced a psychologist teaching their son or daughter the finger trick with regard to multiplying by 9 - and then someone else said, oh yes, I know that one, but the such and such trick is great, too. I don't know any of them! Could you please share?

    Also, when I was in grade school (you can tell how old I am from that statement!), my French teacher taught me a trick re: checking your work on large number multiplication. It was something like adding up all the numbers separately in the products and the result, and keep adding them, and the 9's are counted as 0's and each part should equal the result. Clearly, I can't remember it - but maybe it's enough to get someone here to tell me what it is. I know it helped me throughout school when I was required to multiply large numbers. It's probably outdated, but it was a neat trick.


    #7322 - 01/15/08 05:46 PM Re: Multiplication and Other Math Tricks [Re: questions]
    bianc850a Offline

    Registered: 12/02/07
    Posts: 312
    Loc: California
    Hi Questions,

    I forgot those tricks. However, I remember the title of the book where I saw them. It is called "Math Wizardy for kids" by Margaret Kenda and Phyllis S. Williams. I cannot seem to find the book, but if I happen to find it I will post them. If not, this is a great, fun book to show kids the wonders of math.

    #7323 - 01/15/08 05:51 PM Re: Multiplication and Other Math Tricks [Re: bianc850a]
    questions Offline

    Registered: 11/24/07
    Posts: 864
    Thank you, bianc850a. I'll look for it.

    #7326 - 01/15/08 05:56 PM Re: Multiplication and Other Math Tricks [Re: Dottie]
    questions Offline

    Registered: 11/24/07
    Posts: 864
    Wow! Okay, this is great and will definitely interest DS. Keep em coming. Thanks.

    #7328 - 01/15/08 06:26 PM Re: Multiplication and Other Math Tricks [Re: questions]
    EandCmom Offline

    Registered: 11/09/07
    Posts: 516
    The 9 trick we know is that whatever you are multiplying 9 by, the answer starts with one less that number and then the two numbers add up to 9.

    Example 9 x 2 would be 1 (1 is 1 less than 2) and then 8 as 1 + 8 = 9. So the answer would be 18.

    9 x 3 would be 27 as (2 is 1 less than 3) and (2 + 7 = 9).

    Make sense? It's hard to explain in writing!!! :-)

    #7356 - 01/16/08 08:09 AM Re: Multiplication and Other Math Tricks [Re: EandCmom]
    Grinity Offline

    Registered: 12/13/05
    Posts: 7207
    Loc: Connecticut
    This is giving me flashbacks to when DS11 was in 4th grade. His teacher wrote me a note beaming that DS had shown her a trick for checking to see if a number is divisible by 6.

    Here's the trick:
    1) See if the number is even.
    2) See if the number is divisible by three by using the 'add the digits together and see if that number is divisible by three.'

    I had never thought of combining these two facts into a "6 divisibility trick" as I'm always trying to get to the prime numbers ASAP, but she was totally thrilled. She had never heard that trick before and was so excited.

    I tried to look for a positive explaination, but I was very afraid that DS was getting a 'swelled head' from being phrased for very 'no big deal' things. He already had so many of the signs of underachievment by that point. I tried to put on a calm, mildly positive tone. "What a nice trick, dear, I never thought of it that way." ((shrugs))
    Glad that year is over.

    ((shrugs and more shrugs))

    Coaching available, at


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