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Q&A #6524


Explaining the why's of multiplication place values

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From: Jeanne (for Teacher2Teacher Service)
Date: Jun 18, 2001 at 21:34:05
Subject: Re: Explaining the why's of multiplication place values

Hi Robyn,

Let's look at what 123 means before we multiply.

   123 = 100 + 20 + 3

So, when we mechanically multiply the "2 times 2", we are really
multiplying "20 times 20".

Notice that the multiples of 10, 100, 1000 are lined up.  This makes the
addition easier.  From a mechanical standpoint it looks like we are
just "moving one space to the left."

                  100 + 20 + 3          123
               x  100 + 20 + 3       x  123
               ----------------      -------
                  300 + 60 + 9  ---->   369
           2000 + 400 + 60      ---->  2460
   10000 + 2000 + 300           ----> 12300
   ----------------------------      -------

Hope this helps.


 -Jeanne, for the T2T service

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