Q&A #522

Teaching subtraction

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From: Gail (for Teacher2Teacher Service)
Date: Aug 28, 1998 at 14:50:42
Subject: Re: Teaching subtraction

You might also try dissecting the numbers a bit.  Instead of using the entire
amounts, take just the first three places for a moment ( 100's , 10's, and
1's).  So, the new problem is 900 - 774.  That is a problem that can be
modeled with unit blocks.

If you ask a student to begin with 9 hundreds, and  then "take away" 774, it
is pretty easy to see that something needs to be changed before that can be
done.  When you replace one of the hundreds with 10 tens, you are doing the
regrouping they see on paper.  Taking one of the tens, and replacing it with
10 ones is the next step.  If you ask the student how much they have  when
they have 8 hundreds, 9 tens and 10 ones, they can count to see that they
still have 900, but now it is in a form they can use to complete the problem.

 -Gail, for the Teacher2Teacher service

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