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Q&A #4952


Decomposition in math subtraction

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From: Gail (for Teacher2Teacher Service)
Date: Oct 30, 2000 at 23:09:44
Subject: Re: Decomposition in maths subtraction

Dear Margaret,
    I am glad the explanation helped. What I meant by shorthand was that
we don't usually write out the place values for numbers.  Instead, we let the
place they are in tell that.

So, where we would ordinarily write 359
I wrote out 3 hundreds   5 tens   9 ones.

We definitely wouldn't want to continue to use this method of writing out the
place values in words, because it takes a long time, and isn't really as easy
to work with.  Would we want to switch back and forth between the two
methods?   Well, if a child is having trouble with the way we are trying to
solve a problem, sometimes it is beneficial to back up and show some of the
underlying meanings (which is what we are doing if we write the number words
out), and then try to move back into something more abstract.  If it is still
confusing, we may have to back up again.

As for confusing children, I think they are much more adaptable than we give
them credit for.  They really need to recognize that there are multiple ways
to solve problems, and that there are many ways to write amounts...   for
example, the number we were using before, 359, can be considered as 359 ones,
or 35 tens and 9 ones, or 3 hundreds and 59 ones, or 3 hundreds 5 tens and 9
ones.  It is all dependent upon which of those ways of looking at that amount
is most helpful to us at the moment.  Helping children see multiple ways is a
way of empowering them to be problem solvers.  (now I shall step back down
off my soapbox, before it tips me onto my ear!  :-)
 -Gail, for the T2T service


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